|MP 2.04.10||Identification of Microorganisms Using Nucleic Acid Probes|
|Original Policy Date
|Last Review Status/Date
Reviewed with literature search/9:2014
|Return to Medical Policy Index|
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In the past, identification of microorganisms depended either on culture of body fluids or tissues or identification of antigens, using a variety of techniques including direct fluorescent antibody technique and qualitative or quantitative immunoassays. These techniques are problematic when the microorganism exists in very small numbers or is technically difficult to culture. Indirect identification of microorganisms by immunoassays for specific antibodies reactive with the microorganism is limited by difficulties in
distinguishing between past exposure and current infection; although to some extent immunoglobulin M (IgM) versus IgG antibodies can be helpful. Response to treatment is typically assessed according to the patient’s clinical response or by rising titers of specific antibodies and falling antigen titers.
The availability of nucleic acid probes has permitted the rapid direct identification of microorganisms’ DNA or RNA. Amplification techniques result in exponential increases in copy numbers of a targeted strand of microorganism-specific DNA. The most commonly used amplification technique is PCR or reverse transcriptase (RT)-PCR. In addition to PCR, other nucleic acid amplification techniques have been developed such as transcription-mediated amplification, loop-mediated isothermal DNA amplification
(LAMP), strand displacement amplification, nucleic acid sequence-based amplification, and branched chain DNA signal amplification. After amplification, target DNA can be readily detected using a variety of techniques. The amplified product can also be quantified to give an assessment of how many microorganisms are present. Quantification of the amount of nucleic acids permits serial assessments of response to treatment; the most common clinical application of quantification is the serial measurement of
(HIV RNA (called viral load), which serves as a prognostic factor. (See separate policy on HIV viral load, Policy No. 2.01.22 [archived].) Until 1998, these nucleic acid probe techniques were coded using nonspecific CPT codes describing the multiple steps in the laboratory process. However, in 1998, the CPT codes were revised to include a series of new codes that describe the direct probe technique, amplified probe technique, and quantification for 22 different microorganisms. These series of CPT codes
were introduced as a group; however, at present, probe technologies and clinical applications for some microorganisms are either not widely disseminated or are used primarily for research purposes. In addition, CPT codes have been added for additional microorganisms, such as Staphylococcus aureus. A number of different microorganisms are reviewed as follows.
Bartonella henselae or Quintana
Bartonella henselae or quintana is thought to be responsible for cat scratch disease, which is characterized by chronic regional lymphadenopathy developing about 2 weeks after contact with a cat. A cat scratch skin antigen test is positive in most patients with cat scratch disease, but this test cannot distinguish between active and remote infection.
Bartonella may also cause an opportunistic infection in HIV-infected patients, in whom it is characterized by an acute febrile bacteremic illness, evolving to an asymptomatic bacteremia and finally indolent vascular skin lesions. The organism is typically detected using culture techniques, although an incubation period of 5 to more than 30 days is required. DNA probe technology has been investigated as a diagnostic technique.
Borrelia burgdorferi is responsible for Lyme disease. The clinical symptoms and diagnosis of Lyme disease are more thoroughly discussed in Policy No. 5.01.08 (Intravenous Antibiotic Therapy for Lyme Disease). Antibody assays are typically the first diagnostic laboratory test performed; but these assays may be negative during early disease, and, in the later course of the disease, immunologic assays cannot distinguish between past and present infections, a severe limiting factor in areas of high prevalence. The
spirochete is also difficult to culture, in part because the number of organisms in clinical specimens is extremely low. High sensitivities have been reported from synovial fluid samples; sensitivities of the PCR technique for cerebrospinal fluid, blood, and urine have been disappointing (low and/or variable). Therefore, in some limited instances, PCR amplification has been used to confirm the diagnosis of active Lyme disease.
A commonly occurring yeast, Candida species normally can be found on diseased skin, throughout the entire gastrointestinal tract, expectorated sputum, the female genitalia, and in urine of patients with indwelling Foley catheters. Clinically significant Candida infections are typically diagnosed by clinical observation or by identification of the yeast forms on biopsy specimens. Candida species are a common cause of vaginitis. The diagnosis of vaginitis is addressed separately in Policy No. 2.04.16 (archived).
Chlamydia pneumoniae is an important cause of pneumonia, bronchitis, and sinusitis. Culture and isolation of the microorganism is difficult; a microimmunofluorescence serum test may be used. The use of PCR amplification now offers a rapid diagnosis.
Chlamydia trachomatis is a significant intracellular pathogen causing, most prominently, urogenital disease (including pelvic inflammatory disease) and perinatal infections.
C trachomatis is also responsible for lymphogranuloma venereum. Due to its prevalence and association with pelvic inflammatory disease and perinatal disease, widespread testing of chlamydia is recommended; routine chlamydia testing has been adopted as a quality measure by Healthcare Effectiveness Data and Information Set. This microorganism can be diagnosed by: (1) identifying the typical intracytoplasmic inclusions in cytology specimens; (2) isolation in tissue culture; (3) demonstration of chlamydial antigen by enzyme-linked immunosorbent assay or by immunofluorescent staining; or (4) demonstration of DNA using a direct probe or amplification technique.
Cytomegalovirus (CMV) is a common virus that infects many, but rarely causes clinical disease in healthy individuals. However, this virus can cause protean disease syndromes, most prominently in immunosuppressed patients, including transplant recipients or those infected with the HIV virus. CMV can also remain latent in tissues after recovery of the host from an acute infection. Diagnosis depends on demonstration of the virus or viral components or demonstration of a serologic rise. DNA probe techniques, including amplification, have also been used to identify patients at risk for developing CMV disease as a technique to triage antiviral therapy.
Clostridium difficile is an anaerobic, toxin-producing bacteria present in the intestinal tract. It causes clinical colitis when the normal intestinal flora is altered and overgrowth of C difficile occurs. The common precipitant that disrupts the normal intestinal flora is previous treatment with antibiotics. The disorder has varying severity but can be severe and in extreme cases, life-threatening. C difficile is easily spread from person-to-person contact and is a common cause of hospital-acquired outbreaks. Hospital infection
control measures, such as wearing gloves and handwashing with soap and water, are effective methods of reducing the spread of C difficile. The standard diagnosis is made by an assay for the C difficile cytotoxin or by routine culture methods.
Enteroviruses are single-stranded RNA viruses. This group of viruses includes the polioviruses, coxsackieviruses, echoviruses, and other enteroviruses. In addition to 3 polioviruses, there are more than 60 types of nonpolio enteroviruses that can cause disease in humans. Most people who are infected with a nonpolio enterovirus have no disease symptoms at all. Infected persons who develop illness usually develop either mild upper respiratory symptoms, flu-like symptoms with fever and muscle aches, or an
illness with rash. Less commonly, some persons have "aseptic" or viral meningitis. The use of amplified probe DNA test(s) can be used to detect enteroviruses.
A common microorganism, Gardnerella vaginalis is typically found in the human vagina and is usually asymptomatic. However, G vaginalis is found in virtually all women with bacterial vaginosis and is characterized by inflammation and perivaginal irritation. The microorganism is typically identified by culture. The role of G vaginalis in premature rupture of membranes and preterm labor is also under investigation. Diagnosis of bacterial vaginosis is addressed separately in Policy No. 2.04.16 (archived).
Hepatitis B, C, and G
Hepatitis is typically diagnosed by a pattern of antigen and antibody positivity. However, the use of probe technology permits the direct identification of hepatitis DNA or RNA, which may also provide prognostic information. Quantification techniques are used as a technique for monitoring the response to interferon and/or ribavirin therapy in patients with hepatitis C. The treatment of hepatitis C is addressed in Policy No. 5.01.11 (archived).
Herpes Simplex Virus
Herpes simplex infection of the skin and mucous membranes is characterized by a thin-walled vesicle on an inflammatory base typically in the perioral, ocular, or genital area, although any skin site may be involved. The diagnosis may depend on pathologic examination of cells scraped from a vesicle base or by tissue culture techniques. Herpes simplex encephalitis is one of the most common and serious sporadic encephalitides in immunocompetent adults. The PCR technique to detect herpes simplex virus in the
cerebrospinal fluid has been used to provide a rapid diagnosis of herpes virus encephalitis.
Human herpes virus-6 is widespread in the general population and is also responsible for roseola, a benign rash and fever occurring in young children. HHV-6 may also cause meningitis, encephalitis, pneumonitis, and hepatitis in children and adults. Diagnosis is typically based on rising serologic titers.
HIV-1 and HIV-2
DNA probe technology for HIV-1 is widely disseminated, and HIV-1 quantification has become a standard laboratory test in HIV-1 infected patients. This application is thoroughly discussed in Policy No. 2.01.22 (Plasma HIV-1 RNA Quantification for HIV-1 Infection [archived]). HIV-2 can result in severe immunosuppression and the development of serious opportunistic diseases. Although HIV-2 has been reported in the United States, it is most commonly found in Western Africa. Blood donations are routinely
tested for HIV-2, but due to its rarity in this country, clinical testing for HIV-2 is typically limited to those in contact with persons in a country where HIV-2 is endemic or when the clinical picture suggests HIV infection, but testing for HIV-1 is negative.
Influenza virus is a very common pathogen that accounts for a high burden of morbidity and mortality, especially in elderly and immunocompromised patients. The most common means of identifying influenza is by viral culture, which takes 48 to 72 hours to complete. Influenza is highly contagious and has been the etiology of numerous epidemics and pandemics. Identification of outbreaks is important so that isolation measures may be undertaken to control the spread of disease. Anti-viral treatment can be
effective if instituted early in the course of disease. Therefore, rapid identification of influenza virus is important in making treatment decisions for high-risk patients and in instituting infection control practices.
Legionella pneumophila is among the most common microbial etiologies of community-acquired pneumonia. Laboratory diagnosis depends on culture, direct fluorescent antibody tests, urinary antigens, or DNA probe. DNA probe techniques have also been used in epidemiologic investigations to identify the source of a Legionella outbreak.
Although mycobacterium can be directly identified in sputum samples (ie, acid fast bacilli), these organisms may take 9 to 16 days to culture. DNA probes have also been used to identify specific mycobacterial groups (ie, mycobacterial tuberculosis, avian complex, intracellulare) after culture. In addition, amplification techniques for Mycobacterium tuberculosis may be used in patients who have a positive smear. The rapid identification of M tuberculosis permits prompt isolation of the patient and
identification of the patient’s contacts for further testing.
Mycoplasma pneumoniae is an atypical bacterium that is a common cause of pneumonia. It is most prevalent in younger patients, younger than age 40 years and in individuals who live or work in crowded areas such as schools or medical facilities. The infection is generally responsive to antibiotics of the macrolide or quinolone class. Most patients with M pneumonia recover completely, although the course is sometimes prolonged for up to 4 weeks or more. Extrapulmonary complications of M pneumonia occur
uncommonly, including hemolytic anemia and the rash of erythema multiforme.
Isolation by culture is the conventional form of diagnosis for this common pathogen. Direct DNA probes and amplification techniques have also been used. Neisseria is often tested for at the same time as chlamydia.
Papillomavirus species are common pathogens that produce epithelial tumors of the skin and mucous membranes, most prominently the genital tract. Physical examination is the first diagnostic technique. Direct probe and amplification procedures have been actively investigated in the setting of cervical lesions. The ViraPap test is an example of a commercially available direct probe technique for identifying papillomavirus. Direct probe human papillomavirus (HPV) testing is addressed in Policy No. 2.04.09
(archived). There has also been interest in evaluating the use of viral load tests of HPV to identify patients at highest risk of progressing to invasive cervical carcinoma.
Streptococcus, Group A
Also referred to as Streptococcus pyogenes, this pathogen is the most frequent cause of acute bacterial pharyngitis. It can also give rise to a variety of cutaneous and systemic conditions, including rheumatic fever and post-Streptococcal glomerulonephritis. Throat culture is the preferred method for diagnosing Streptococcus pharyngitis. In addition, a variety of commercial kits are now available that use antibodies for the rapid detection of group A carbohydrate antigen directly from throat swabs. While very specific,
these kits are less sensitive than throat cultures, so a negative test may require confirmation from a subsequent throat culture. DNA probes have also been used for direct identification of streptococcus and can be used as an alternative to a throat culture as a back-up test to a rapid, office-based strep test.
Streptococcus, Group B
Also referred to as Streptococcus agalactiae, Streptococcus, group B (GBS) is the most common cause of sepsis, meningitis, or death among newborns. Early-onset disease, within 7 days of birth, is related to exposure to GBS colonizing the mother’s anogenital tract during birth. The Centers for Disease Control and Prevention, the American College of Obstetrics and Gynecology, and the American Academy of Pediatricians recommend either maternal risk assessment or screening for GBS in the perinatal period.
Screening consists of obtaining vaginal and anal specimens for culture at 35 to 37 weeks of gestation. The conventional culture and identification process requires 48 hours. Therefore there has been great interest in developing rapid assays using DNA probes to shorten the screening process, so that screening could be performed in the intrapartum period with institution of antibiotics during labor.
Trichomonas is a single-cell protozoan that is a common cause of vaginitis. The organism is sexually transmitted and can infect the urethra or vagina. The most common way of diagnosing trichomonas is by clinical signs and by directly visualizing the organism by microscopy in a wet prep vaginal smear. Culture of trichomonas is limited by poor sensitivity. Treatment with metronidazole results in a high rate of eradication. The disease is usually self-limited without sequelae, although infection has been associated
with premature birth and higher rates of HIV transmission, cervical cancer, and prostate cancer.
A list of current U.S. Food and Drug Administration (FDA)‒approved or cleared nucleic acid-based microbial tests is available at: http://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/InVitroDiagnostics/ucm330711.htm
The Association of Molecular Pathology (AMP) website also provides a list of current FDA approved tests for diagnosis of infectious diseases (available online at: http://www.amp.org/FDATable/FDATable.pdf). Table 2 lists tests that are FDA-approved/cleared but do not have specific CPT codes.
Table 2. FDA-Approved/Cleared Tests without CPT codes
FDA Approved/Cleared Diagnostic Test
Coxiella burnetii (Q fever)
PNA (Peptide nucleic acid) FISH
Escherichia coli and Pseudomonas aeruginosa
Escherichia coli and/or Klebsiella pneumoniae and Pseudomonas aeruginosa
Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa
Multiplex Real-time RT-PCR
Multiplex Real-time RT-PCR
Influenza virus A/H5
Influenza virus H1N1
FDA: Food and Drug Administration; FISH: fluorescence in situ hybridization; PCR: polymerase chain reaction; PNA: peptide nucleic acid; RT: reverse transcriptase.
The status of nucleic acid identification using direct probe, amplified probe, or quantification for the microorganisms listed in the CPT book are summarized in Table 1:
Table 1. Status of Nucleic Acid Probes
|Bartonella henselae or quintana||87470 (inv)||87471(inv)||87472 (inv)|
|Borrelia burgdorferi1||87475 (inv)||87476 (inv)||87477 (inv)|
|Candida species (see policy No. 2.04.16 - archived)||87480 (med nec)||87481 (med necinv)||87482 (inv)|
|Chlamydia pneumoniae||87485 (inv)||87486 (inv)||87487 (inv)|
|Chlamydia trachomatis||87490 (med nec)||87491 (med nec)||87492 (inv)|
|Clostridium difficile||87493 (med nec)|
|Cytomegalovirus||87495 (med nec)||87496 (med nec)||87497 (med nec)|
|Enterococcus, Vancomycin-resistant (e.g., enterococcus vanA, vanB)||87500 (med nec)|
|Gardnerella vaginalis (see policy No. 2.04.16 - archived)||87510 (med nec)||87511 (inv)||87512 (inv)|
|Gastrointestinal Pathogen Panel||87505-87507 (inv)|
|Hepatitis B||87515 (med nec)||87516 (med nec)||87517 (med nec)|
|Hepatitis C||87520 (med nec)||87521 (med nec)||87522 (med nec)|
|Hepatitis G||87525 (inv)||87526 (inv)||87527 (inv)|
|Herpes simplex virus||87528 (med nec)||87529 (med nec)||87530 (inv)|
|Herpes virus-6||87531 (inv)||87532 (inv)||87533 (inv)|
|Human Immunodeficiency Virus 1 (HIV-1)||87534 (med nec)||87535 (med nec)||87536 (med nec)|
|Human Immunodeficiency Virus 2 (HIV-2)||87537 (med nec)||87538 (med nec)||87539 (med nec)|
|Human Papillomavirus (HPV) (see also policy No. 2.04.09)||87620 (med nec)||87621 (med nec)||87622 (inv)|
|Influenza virus||87501 (med nec)||87502 (med nec)||87503 (med nec)|
|Legionella pneumophila||87540 (inv)||87541 (inv)||87542 (inv)|
|Mycobacterium species||87550 (med nec)||87551 (inv)||87552 (inv)|
|Mycobacterium tuberculosis||87555 (med nec)||87556 (med nec)||87557 (inv)|
|Mycobacterium avium intracellulare||87560 (med nec)||87561 (inv)||87562 (inv)|
|Mycoplasma pneumoniae||87580 (inv)||87581 (inv)||87582 (inv)|
|Neisseria gonorrhoeae||87590 (med nec)||87591 (med nec)||87592 (inv)|
|Respiratory virus panel||87631-87633 (med nec)|
|Staphylococcus aureus||87640 (med nec)|
|Staphylococcus aureus, methicillin resistant||87641 (med nec)|
|Streptococcus group A*||87650 (med nec)||87651 (inv)||87652 (inv)|
|Streptococcus group B||87653 (med nec)|
|Trichomonas vaginalis||87660 (med nec)||87661 (med nec)|
inv: investigational; med nec: medically necessary.
aThese probes are investigational except as noted in other policies, see reference Policy No. 5.01.08.
bThe direct DNA probe test for streptococcus A is designed to be an alternative to a confirmatory culture. Therefore, the simultaneous use of confirmatory culture and DNA probe test is considered not medically necessary. Antibiotic sensitivity of streptococcus A cultures is frequently not performed for throat cultures. However, if an antibiotic sensitivity is considered, then the most efficient method of diagnosis would be a combined culture and antibiotic sensitivity.
cFor uncomplicated infections, testing for only 1 candida species, C albicans, may be considered medically necessary. For complicated infections, testing for multiple candida subspecies may be considered medically necessary. The Centers for Disease Control and Prevention classifies uncomplicated vulvovaginal candidiasis as being sporadic or infrequent or mild to moderate or likely to be C albicans or in nonimmunocompromised women. Complicated vulvovaginal candidiasis is classified as being recurrent or severe or not a C. albicans species or in women with uncontrolled diabetes, debilitation or immunosuppression.1
CPT codes 87797, 87798, and 87799 describe the use of direct probe, amplified probe, and quantification, respectively, for infectious agents not otherwise specified. A discussion of every infectious agent that might be detected with a probe technique is beyond the scope of this policy.
It should be noted that the technique for quantification includes both amplification and direct probes; therefore, simultaneous coding for both quantification with either amplification or direct probes, is not warranted.
In the evaluation of Group B streptococcus, the primary advantage of a DNA probe technique compared to traditional culture techniques is the rapidity of results. This advantage suggests that the most appropriate use of the DNA probe technique is in the setting of impending labor, for which prompt results could permit the initiation of intrapartum antibiotic therapy.
Many probes have been combined into panels of tests. For the purposes of this policy, other than the respiratory virus panel, only individual probes are reviewed.
BlueCard/National Account Issues
Plans may wish to identify specific sites of service (i.e., hospital, reference laboratory, etc.).
Plans may review benefits for test panels by evaluating individual components of the panel.
This policy was originally created in 1998 and has regularly been updated with literature reviews. The most recent literature review was conducted for the period of July 2013 through August 23, 2014.
Although nucleic acid probe technologies offer the potential for rapid, sensitive detection for a variety of microorganisms, there are many technologic limitations, and the clinical application of these techniques is still developing. This technology requires the identification and manufacture of nucleic acid probes, ie, short strands of either DNA or RNA that are specific to the target microorganism. Amplification requires the use of specific short segments of complementary DNA, called primers, to initiate the repetitive rounds of DNA duplication. For many of the microorganisms, these probes or primers are not commercially
available, and different reference laboratories may use different products. Early amplification techniques of polymerase chain reaction (PCR) raised considerable concerns regarding contamination from one specimen to another, creating the potential for false positive results. Nonspecific amplification is also a
concern related in part to the specificity of the probes used. The clinical interpretation of results may also be challenging. Amplification of organisms representing latent infection or colonization cannot be distinguished from active, clinically significant infections. In addition, amplification techniques may amplify
fragments of nucleic acids, representing dead microorganisms, thus further clouding the clinical interpretation. Finally, specificities, sensitivities, and positive (PPV) and negative predictive values (NPV) have not been reported in large groups of patients for many of the microorganisms. Newer nucleic acid
amplification techniques have been developed to reduce concerns regarding possible laboratory cross contamination and improve the clinical relevance of test results with higher sensitivity rates.
In general, nucleic acid probe techniques are used when traditional culture is difficult due to the low numbers of the organisms (ie, HIV), fastidious or lengthy culture requirements (ie, mycobacterium, chlamydia, neisseriae), or difficulty in collecting an appropriate sample (herpes simplex encephalitis).
2-5 Quantification is a useful clinical tool when the viral load can be used as a prognostic indicator or to follow the patient’s response to therapy; this is an established practice in patients with HIV or hepatitis C. The clinical utility and medical necessity of these probes will be determined in part by the accuracy of the test (sensitivity, specificity, and predictive value) compared with standard identification techniques. The rapidity of results will also be considered, with the clinical utility of early identification considered in the context of each clinical situation to determine medical necessity.
Bartonella henselae or Quintana
Microbiologic detection of Bartonella henselae or quintana is difficult, and molecular testing is not readily available. However, a monoclonal antibody (mAB) to B henselae has become commercially available. A 2009 study6 evaluated the usefulness of immunohistochemical analysis (IHC) for diagnosing B henselae on surgical specimens and compared these results with PCR detection and serologic testing. The study included 24 formalin-fixed, paraffin-embedded (FFPE) cases of lymphadenitis with histologic and/or clinical suspicion of B henselae. Control cases included 14 cases of lymphadenopathy. FFPE tissue sections were evaluated with a mAB to B henselae, Steiner silver stain (SSS), and PCR that targeted B henselae and B quintana. Positive cases were as follows: SSS, 11 (46%); PCR, 9 (38%); and IHC, 6 (25%). Only 2 cases (8%) were positive for all 3 techniques. All control cases were negative for IHC and
PCR. The diagnostic sensitivity of these 3 tests is low for bartonellae. SSS seems to be the most sensitive test but is the least specific. PCR is more sensitive than IHC and may, therefore, serve as a helpful second-line test on all IHC negative cases.
DNA probes are available to aid in diagnosis of Lyme disease caused by Borrelia burgdorferi in limited circumstances. Cerebrospinal fluid may be positive by PCR during the first 2 weeks of infection, but thereafter the detection rate is low. PCR is not recommended for urine or blood specimens. However,
PCR-based direct detection of B burgdorferi in the blood may be useful for documenting Lyme carditis when results of serologic studies are equivocal. A 2012 study7 evaluated the sensitivity of 5 direct diagnostic methods (culture and nested PCR of a 2-mm skin biopsy specimen, nested PCR, and
quantitative PCR [qPCR] performed on the same 1-mL aliquot of plasma and a novel qPCR-blood culture method) in 66 untreated adult patients with erythema migrans, the most common clinical manifestation. The results found 1 or more of these tests were positive in 93.9% of the patients. Culture was more
sensitive than PCR for both skin and blood, but the difference was only statistically significant for blood samples (p<0.005). Blood culture was significantly more likely to be positive in patients with multiple erythema migrans skin lesions compared with those with a single lesion (p=0.001). Positive test results
among the 48 patients for whom all 5 assays were performed invariably included either a positive blood or a skin culture. Results of this study demonstrated that direct detection methods such as PCR and culture are highly sensitive in untreated adult patients with erythema migrans. Erythema migrans eventually
resolves even without antibiotic treatment. However, the infecting pathogen can spread to other tissues and organs, causing more severe manifestations that can involve a patient's skin, nervous system, joints, or heart. Diagnosed cases are usually treated with antibiotics for 2 to 4 weeks, and most patients make
an uneventful recovery. 8 Therefore, laboratory evidence of infection is essential for diagnosis, except in the case of typical erythema migrans.
Candida infections are most commonly caused by Candida albicans but other species may be responsible. In complicated or severe cases, eg, candidemia and invasive focal infections, or in compromised patients, it may be necessary to identify the infecting Candida species for appropriate
treatment planning. DNA probes are available to aid in the diagnosis of possible Candida species infections. Amplified peptide nucleic acid tests have demonstrated high sensitivity and specificity levels of up to 100%. 9,10 Some tests have been able to detect up to 6 Candida species.11 A real-time qPCR assay,
developed for the detection of the most common pathogenic Candida species using a single-reaction PCR assay targets a selected region of the 28S subunit of the fungal rDNA gene. In a 2012 study, the sensitivity and specificity of an assay based on quantitative real-time assay using duplex mutation primers
were 100% and 97.4%, respectively. 10 The data suggest that this assay may be appropriate for use in clinical laboratories as a simple, low-cost, and rapid screening test for the most frequently encountered Candida species.
Vulvovaginal candidiasis can typically be diagnosed by microscopy, and most cases are caused by Calbicans. Other species, such as Candida glabrata, may be responsible but are less common and may be difficult to detect by microscopy. Therefore, identification of Candida subspecies is not usually
necessary and should be limited to use in complicated, recurrent or persistent cases that are resistant to azole/antifungal treatment. Additionally, symptomatic patients with negative microscopy may warrant subspecies testing.1
Chlamydia pneumonia or Trachomatis
Probes are commercially available for the detection of Chlamydia pneumonia or trachomatis. A 2011 study8 demonstrated a Chlamydia-specific real-time PCR which targeted the conserved 16S rRNA gene.
The test can detect at least 5 DNA copies and shows very high specificity without cross-amplification from other bacterial DNA. The PCR was validated with 128 clinical samples positive or negative for Chlamydia trachomatis or C pneumoniae. Of 65 positive samples, 61 (93.8%) were found to be positive with the new PCR. Another study12 demonstrated the VERSANT® CT/GC DNA 1.0 Assay performed with 99.2% specificity for Chlamydia trachomatis detection and sensitivity of 100%. As a clinical consideration, patients with suspected C trachomatis accept antibiotic treatment before their infection status had been
confirmed. Treatment of individuals with C trachomatis genital infection prevents sexual transmission and complications, including pelvic inflammatory disease. Treatment of pregnant women will prevent the transmission of infection to infants during delivery. The benefits of treatment of respiratory infections due
to C pneumoniae are more difficult to assess, primarily because of the lack of U.S. Food and Drug Administration (FDA)‒approved, specific diagnostic tests for detection of the organism in clinical samples. 13
DNA probes for Clostridium difficile using PCR have been commercially available since 2009.14-17 Eastwood et al15 compared the performance characteristics of numerous DNA probes with cytotoxic assays and cultures. The results demonstrated a mean sensitivity of 82.8% (range, 66.7%-91.7%) and a
mean specificity of 95.4% (range, 90.9%-98.8%). Rapid identification of C difficile allows for early treatment of the disease and timely institution of isolation measures to reduce transmission. Because of the advantages of early identification of C difficile, these probes may be considered medically necessary.
There is interest in using viral load tests for cytomegalovirus (CMV), specifically to identify asymptomatic immunosuppressed patients (ie, transplant recipients) who would be candidates for preemptive antiviral therapy. For example, among transplant recipients, CMV infections account for about two-thirds of deaths in the immediate posttransplant period (ie, up to 50 days posttransplant), and thus, a variety of preventive therapies have been investigated. One strategy proposes that all at-risk patients (ie, seropositive patients, or seronegative patients receiving a seropositive organ) be treated prophylactically with antiviral therapy during the first 100 days after transplantation. While this strategy has been shown to be effective in reducing the risk of CMV disease, it results in a large number of patients being treated unnecessarily. Therefore, preemptive therapy has become an accepted option, in which antiviral therapy is initiated when a laboratory technique identifies an increasing viral load. Late CMV disease, defined as occurring after 100 days, is also a concern, and viral loads can also be monitored to prompt antiviral therapy. A variety of laboratory techniques are available to evaluate viral loads. For example, pp65 antigenemia refers to a fluorescent antigen detection technique that identifies an antigen specific to CMV. However, this test is described as labor intensive and requiring specialized personnel for interpretation, and thus, a variety of tests to detect CMV DNA have been developed, including but not limited to Hybrid Capture (Digene Corp.), Amplicor CMV Monitor Tests (Roche Molecular System), and TaqMan. The specific techniques used may vary by local availability, but studies have suggested that all provide complementary information.18-22
Amplified DNA probes are available for detecting this group of viruses including the polioviruses, coxsackieviruses, echoviruses, and other enteroviruses. In addition to 3 polioviruses, there are more than 60 types of nonpolio enteroviruses that can cause disease in humans. Several FDA-approved test kits are
available including the GeneXpert Enterovirus Assay (GXEA), with a sensitivity, specificity, PPV and NPV of 82.1%, 100%, 100%, and 96.2%, respectively. In this study, molecular assays were superior to viral culture for detecting Enterovirus RNA in cerebrospinal fluid. GXEA showed a high specificity but a lower
sensitivity for the detection of Enterovirus RNA compared with the RT-qPCR assay.23 Management is supportive and addresses symptoms. No antiviral medications are currently approved for the treatment of Enterovirus infections. These amplified probes can be part of a panel that includes other respiratory
viruses (see Respiratory Viral Panel section).
Probes are available for detecting vancomycin resistance of organisms (eg, for Enterococcus). These probes are able to detect vancomycin resistance in a rapid and accurate manner so that appropriate antibiotic selection can be made and infectious precautions, such as isolation, can be instituted.
A 2006 study26 evaluated vaginal specimens, from 321 symptomatic women, that were analyzed for bacterial vaginosis by both Gram stain using Nugent criteria and a DNA hybridization test (Affirm VPIII hybridization test). Of the 321 patients, 115 (35.8%) were Gram-positive for bacterial vaginosis and 126
(39.2%) were negative. A total of 80 patients (25.0%) demonstrated intermediate Gram staining that was also considered negative. The DNA hybridization test detected Gardnerella vaginalis in 107 (93.0%) of 115 vaginal specimens positive for bacterial vaginosis diagnosed by Gram stain. Compared with the
Gram stain, the DNA hybridization test had a sensitivity of 87.7% and a specificity of 96.0%. PPVs and NPVs of the DNA hybridization test were 93.0% and 92.7%, respectively. The study concluded the Affirm VPIII hybridization test correlated well with Gram stain and may be used as a rapid diagnostic tool to
exclude bacterial vaginosis in women with genital complaints.
Gastrointestinal Pathogen Panel
Infectious gastroenteritis may be caused by a broad spectrum of pathogens resulting in the primary symptom of diarrhea. Panels for gastrointestinal pathogens uses multiplex amplified probe techniques and multiplex reverse transcription for the simultaneous detection of many gastrointestinal pathogens
such as C difficile, Escherichia coli, Salmonella, Shigella, norovirus, rotavirus, and Giardia. Several studies of gastrointestinal pathogen panels demonstrate overall high sensitivities and specificities and indicate the panels may be useful for detecting causative agents for gastrointestinal infections.
27,28 Access to a rapid method for etiologic diagnosis of gastrointestinal infections may lead to more effective early treatment and infection control measures, but further studies are needed.
Viral load has also been investigated in patients with hepatitis B receiving the antiviral therapy lamivudine. Research interest has focused on assessing response to therapy and identifying the emergence of resistant strains of hepatitis B.29-32 Although clearly, many aspects of viral load measurements in hepatitis
B are primarily research tools, it does appear that measurements of viral load may be used to determine when to initiate therapy. For example, treatment may not be required in asymptomatic Hbe-Ag-negative patients with normal liver enzymes who have a viral load below 10 to 5 genomes per milliliter. In contrast, there are questions about how viral load measurements should be used to monitor the response to therapy.33
Diagnostic tests for hepatitis C can be divided into 2 general categories: (1) serological assays that detect antibody to hepatitis C virus (anti-HCV); and (2) molecular assays that detect, quantify, and/or characterize HCV RNA genomes within an infected patient. Detection of HCV RNA in patient specimens
by PCR provides evidence of active HCV infection and is potentially useful for confirming the diagnosis and monitoring the antiviral response to therapy. Two main technologies exist for assessing HCV RNA levels or viral load. Quantitative PCR is the most sensitive test for determining hepatitis C viral load.
Molecular tests have also been developed to classify HCV into distinct genotypes; the clinical importance of HCV genotype is related directly to treatment options. After the introduction of the HCV RNA PCR test, it became clear that interferon therapy can cure HCV infections in a certain number of patients.
Widespread therapy was introduced after a co-drug ribavirin was found to reduce relapse rates, and 2 pivotal trials with recombinant interferon showed sustained virologic responses in about 50% of patients, with much higher positive outcomes in genotype 2 and 3.34 Therapy-induced sustained virologic remission has been shown to reduce liver-related death, liver failure, and to a lesser extent hepatocellular carcinoma.
It is possible that hepatitis C is part of a group of GB viruses, rather than just a single virus. It is unclear if hepatitis G causes a type of acute or chronic illness. When diagnosed, acute hepatitis G infection has usually been mild and brief and there is no evidence of serious complications, but it is possible that, like
other hepatitis viruses, it can cause severe liver damage resulting in liver failure. The only method of detecting hepatitis G is by real-time PCR and direct sequencing for 4 randomly selected samples followed by phylogenetic analysis.
Herpes Simplex Virus
Typing of HSV isolates is required to identify the virus isolated in culture. The methods available for this include antigen detection by immunofluorescence (IF) assays and PCR. A 2009 cross-sectional study35 utilized 4 reference strains and 42 HSV isolates obtained from patients between September 1998 and
September 2004. These were subjected to testing using a MAb-based IF test and a PCR that detects the polymerase (pol) gene of HSV isolates. The observed agreement of the MAb IF assay with the pol PCR was 95.7%. A total of 54.8% (23/42) of isolates tested by IF typing were found to be HSV-1, 40.5%
(17/42) were HSV-2, and 2 (4.8%) were untypable using the MAb IF assay. The 2 untypable isolates were found to be HSV-2 using the pol PCR. According to the American Academy of Family Physicians, antiviral medications have expanded treatment options for the 2 most common cutaneous manifestations, HSV-1 and HSV-2. Acyclovir therapy remains an effective option; however, famciclovir and valacyclovir offer improved oral bioavailability and convenient oral dosing schedules but at a higher cost. Patients who have 6 or more recurrences of genital herpes per year can be treated with daily regimens which are
effective in suppressing 70% to 80% of symptomatic recurrences.
Herpes virus-6 is the common collective name for human herpesvirus 6A (HHV-6A) and human herpesvirus 6B (HHV-6B). These closely related viruses are 2 of the 9 herpesviruses known to have humans as their primary host. HHV-6A has been described as more neurovirulent36 and as such, is more
frequently found in patients with neuroinflammatory diseases, such as multiple sclerosis.37 HHV-6B primary infection is the cause of the common childhood illness exanthem subitum. Additionally, HHV-6B reactivation is common in transplant recipients, which can cause several clinical manifestations such as
encephalitis, bone marrow suppression and pneumonitis.38
Human Immunodeficiency Virus 1
Validated DNA probes are widely available for diagnosis and HIV-1 quantification. Quantification is regularly done to determine viral load in infected patients to monitor response to antiretroviral therapies.
Human Immunodeficiency Virus 2
DNA probes are available for diagnosis and quantification of HIV-2. HIV-2 is most commonly found in Western Africa, although it has been reported in the United States. Blood donations are routinely tested for HIV-2, but clinical testing for HIV-2 is typically limited to those in contact with persons in a country
where HIV-2 is endemic or when clinical evaluation suggests HIV infection, but testing for HIV-1 is negative. HIV-2 quantification is regularly done to determine viral load in infected patients to monitor response to antiretroviral therapies.
There has also been research interest in exploring the relationship of human papilloma viral load and progression of low-grade cervical lesions to cervical cancer. While studies have reported that high-grade lesions are associated with higher viral loads,39,40 clinical utility is based on whether or not the presence of increasing viral loads associated with low-grade lesions is associated with disease progression. For example, current management of cervical smears with “atypical cells of uncertain significance” suggests testing with HPV , and then, if positive, followed by colposcopy. It is hypothesized that colposcopy might
be deferred if a low viral load were associated with a minimal risk. However, how treatment decisions may be tied to measurements of viral load is unclear.41-43 Persistent infection with various HPV genotypes has also been linked with cervical lesions and may influence treatment decisions. HPV genotypes 16 and 18 have been most associated with carcinogenesis. Patients with high-risk HPV genotypes may warrant direct referral to colposcopy.44,45
|CPT||See Policy section above|
|ICD-9 Procedure||No code|
|ICD-9 Diagnosis||010.0 – 018.9||Tuberculosis, code range|
|030.0 – 030.9||Diseases due to infection by Mycobacterium leprae|
|031.0 – 031.9||Diseases due to other mycobacteria (includes mycobacterium avium-intracellualare)|
|041.84||Other specified bacterial infections - other anaerobes (includes clostridium NEC)|
|042||Human immunodeficiency virus (HIV) disease, symptomatic|
|054.0 – 054.9||Herpes simplex, code range|
|070.20 – 070.33||Viral hepatitis B, code range|
|070.41||Acute or unspecified hepatitis C with hepatic coma|
|070.44||Chronic hepatitis C with hepatic coma|
|070.51||Acute or unspecified hepatitis C without mention of hepatic coma|
|070.54||Chronic hepatitis C without mention of hepatic coma|
|079.88||Other specified chlamydial infection|
|079.89||Other specified viral infections (includes papillomavirus)|
|079.98||Unspecified chlamydial infection|
|098.0 – 098.89||Gonococcal infections, code range|
|131.00-131.09||Urogenital trichomoniases, code range|
|487.0-488.19||Influenza, code range|
|771.1||Congenital cytomegalovirus infection|
|771.2||Other congenital infections (includes herpes simplex, tuberculosis)|
|V08||Human immunodeficiency virus (HIV) asymptomatic|
|V28.6||Antenatal screening for Streptococcus B|
|ICD-10-CM (effective 10/1/15)||A04.7||Enterocolitis due to Clostridium difficile|
|A15.0 – A19.9||Tuberculosis, code range|
|A30.0 – A30.9||Leprosy, code range|
|A31.0 – A31.9||Mycobacteria infection, code range|
|A48.1 – A48.2||Legionnaires’ disease, code range|
|A54.0 – A54.9||Gonococcal infection, code range|
|A59.00-A59.09||Urogenital trichomoniasis, code range|
|A74.81 – A74.89||Other chlamydial diseases|
|A74.9||Chlamydial infection, unspecified|
|B00.0 – B00.9||Herpesviral simplex, code range|
|B16.0 – B16.9||Acute hepatitis B with Delta-agent, code range|
|B17.10 – B17.11||Acute viral hepatitis C, code range|
|Chronic viral hepatitis B, code range|
|B18.2||Chronic viral hepatitis C|
|B19.10 – B19.11||Unspecified viral hepatitis B, code range|
|B19.20 – B19.21||Unspecified viral hepatitis C, code range|
|B25.0 – B25.9||Cytomegaloviral disease, code range|
|J09.010-J11.89||Influenza, code range|
|P35.0-P35.9||Congenital viral diseases, code range (includes cytomegalovirus, herpesviral, hepatitis, other and unspecified viral diseases)|
|Z36||Encounter for antenatal screening of mother|
|ICD-10-PCS (effective 10/1/15)||Not applicable. ICD-10-PCS codes are only used for inpatient services. There are no ICD procedure codes for laboratory tests.|
|Type of Service||Pathology/Laboratory|
|Place of Service||Inpatient/Outpatient|
Clostridium difficile, Diagnosis
Herpes Simplex, Diagnosis
Herpes Virus-6, Diagnosis
Neisseria Gonorrhoeae, Diagnosis
Trichomonas vaginalis, Diagnosis
|07/10/98||Add policy to Medicine section||New policy|
|03/15/99||Replace policy||Corrected CPT codes for Mycobacterium species|
|02/18/00||Replace policy||Policy revised; new policy statement on viral load test for hepatitis C|
|12/15/00||Replace policy||Correction – in the table on page 5, 3rd line from the bottom (Papillomavirus) – the 3rd code should be 87622 not 87623|
|8/15/01||Replace policy||New policy on Strep A; direct probe test|
|12/17/03||Replace policy||Policy revised with focus on viral load tests (i.e., quantitation). Policy statement revised to indication of quantitation of CMV (CPT code 87497) now considered medically necessary|
|04/1/05||Replace policy||Policy revised with focus on viral load tests for hepatitis B and papilloma virus. Policy revised to state that viral load for hepatitis B can be considered medically necessary (CPT code 87517). Reference number 14 added; rest of policy unchanged|
|09/27/05||Replace policy||Policy revised with focus on DNA tests for Group B streptococcus, now considered medically necessary. Reference numbers 21 and 22 added and ICD-9 code for antenatal screening for Group B streptococcus|
|04/17/07||Replace policy||Policy updated with literature search. Medically necessary indications added for Staphylococcus aureus and methicillin resistant Staph aureus. New CPT codes added. Reference numbers 23 and 24 added|
|06/12/08||Replace policy||Policy updated with literature search. Medically necessary indication added for vancomycin resistance (e.g. enterococcus). New CPT code (87500) and reference numbers 25 and 26 added.|
|9/1/11||Replace policy||Policy updated with literature search. Medically necessary indications added for clostridium difficile and influenza virus. References 27-36 added.|
|09/13/12||Replace policy||Policy updated with literature search. References 5-11, 21, 24, 30-34, 42-45, 48-52, 56 added. New information added to rationale for numerous probes. New medically necessary indication added for respiratory virus panel amplified probes.|
|9/12/13||Replace policy||Policy updated with literature search through July 2013. Candida species amplified probe 87481 changed from investigational to medically necessary. Medically necessary indication for Trichomonas vaginalis amplified probe added. References 8, 10 and 62-63 added.|
|9/11/14||Replace policy||Policy updated with literature review through August 23, 2014. Added gastrointestinal pathogen panel as investigational to the policy statement. New CPT codes (8751XX 1-3 and 876XX 3-5) and references 1, 27-28, 44-45, and 63-64 added.|
Numerous different strains of influenza virus can be identified by DNA probes. Published studies indicate improved sensitivity of PCR for identifying influenza and distinguishing influenza from related viruses. Lassauniere et al46 used a multiplex RT-PCR probe to identify 13 respiratory viruses, including influenza A and B. Screening of 270 samples that were negative on immunofluorescence assays revealed the presence of a respiratory virus in 44.1%. Probes have also been developed to identify specific strains of influenza associated with epidemics, such as the H1N1 influenza virus.47 Because of the importance of early identification of outbreaks for infection control purposes, use of this test may be considered medically necessary.
DNA probes for Legionella pneumophila have been developed. A recent study48 compared the usefulness of 2 quantitative RT-PCR assays (qrt-PCRmip targeting L pneumophila, and qrt-PCR16S targeting all Legionella species) performed on lower respiratory tract (LRT) samples for diagnostic and prognostic purposes in 311 patients hospitalized for community-acquired pneumonia (CAP). The Now Legionella urinary antigen test from Binax (Portland, ME) was used as a reference test. One subset of 255 CAP patients admitted to Chambery hospital in 2005 and 2006 was evaluated and the sensitivities, specificities, PPVs and NPVs for both qrt-PCR tests were 63.6%, 98.7%, 77.7%, and 97.4%, respectively. High bacterial loads in LRT samples at hospital admission were significantly associated with the need for hospitalization in an intensive care unit and for prolonged hospitalization.
DNA probes are available to distinguish between Mycobacterium species. In a recent study,49 the extracted DNA specimens from Mycobacterium species and non-Mycobacterial species were tested using peptide nucleic acid (PNA) probe-based RT-PCR assay to evaluate potential cross-reactivity. A total of 531 respiratory specimens (482 sputum specimens, 49 bronchoalveolar washing fluid specimens) were collected from 230 patients in July and August, 2011. All specimens were analyzed for the detection of Mycobacteria by direct smear examination, mycobacterial culture, and PNA probe-based RT-PCR assay. In cross-reactivity tests, no false positive or false negative results were evident. When the culture method was used as the criterion standard test for comparison, PNA probe-based RT-PCR assay for detection of Mycobacterium tuberculosis complex (MTBC) had a sensitivity and specificity of 96.7% (58/60) and 99.6% (469/471), respectively. Assuming the combination of culture and clinical diagnosis as the standard, the sensitivity and specificity of the RT-PCR assay for detection of MTBC were 90.6% (58/64) and 99.6% (465/467), respectively. The new RT-PCR for the detection of nontuberculous mycobacteria ad a sensitivity and specificity of 69.0% (29/42) and 100% (489/489), respectively.
DNA probes are available to diagnose Mycobacterium tuberculosis infection. In a recent study,50 an inhouse IS6110 RT-PCR (IH IS6110), MTB Q-PCR Alert (Q-PCR) and GenoType® MTBDRplus (MTBDR) were compared for the direct detection of (MTBC in 87 specimens. This included 82 first smear-positive specimens and 3 smear-negative specimens. The sensitivities of IH IS6110, Q-PCR, MTBDR, and IH ITS for MTBC detection were 100%, 92%, 87%, and 87% respectively, compared with culture. Both IS6110- based RT-PCRs (in-house and Q-PCR) were similar in performance with 91.2% concordant results for MTBC detection. However, none of the RT-PCR assays tested provide drug resistance data. Detection and drug resistance profiling are necessary for successful treatment of infection.
Mycobacterium avium and Mycobacterium intracellulare
DNA probes are available to diagnose Mycobacterium avium and Mycobacterium intracellulare infection. A recent study51 evaluated the performance of the GenoType Mycobacteria Direct (GTMD) test for rapid molecular detection and identification of the MTBC and 4 clinically important nontuberculous mycobacteria (M avium, M intracellulare, M kansasii, M malmoense) in smear-negative samples. A total of 1570 samples (1103 bronchial aspiration, 127 sputum, 340 extrapulmonary samples) were analyzed. When evaluated, the performance criteria in combination with a positive culture result and/or the clinical outcome of the patients, the overall sensitivity, specificity, and PPVs and NPVs were found to be 62.4%, 99.5%, 95.9%, and 93.9%, respectively, whereas they were 63.2%, 99.4%, 95.7%, and 92.8%, respectively, for pulmonary samples and 52.9%, 100%, 100%, and 97.6%, respectively, for extrapulmonary samples. Among the culture-positive samples which had Mycobacterium species detectable by the GTMD test, 3 samples were identified to be M intracellulare and 1 sample was identified to be M avium. However, 5 M intracellulare samples and an M kansasii sample could not be identified by the molecular test and were found to be negative. The GTMD test is a reliable, practical, and easy tool for rapid diagnosis of smear-negative pulmonary and extrapulmonary tuberculosis so that effective precautions may be taken and appropriate treatment may be initiated.
Probes for Mycoplasma pneumonia have been developed. 52,53 Chalker et al52 tested 3987 nose and throat swabs from patients presenting with symptoms of a respiratory tract infection. Mycoplasma DNA was present in 1.7% of patients overall and was more common in children aged 5 to 14 years, in whom
6.0% of samples were positive. Probes have also been developed to test for mycoplasma strains with macrolide resistance. Peuchant et al53 found that 9.8% (5/51) of mycoplasma strains were macrolide resistant. However, the clinical utility of this probe is uncertain given that the disease is usually selflimited.
It is unclear whether early identification of mycoplasma, and/or identification of resistance, leads to improved outcomes.
Probes for Neisseria gonorrhoeae have been developed for commercial use. These probes are often a combination test with C trachomatis. A recent study54 demonstrated the PPV of the screening PCR (cobas 4800 CT/NG PCR screening assay) in urine specimens remained high (98.75%) even though the
prevalence of gonorrhoeae was low. Another study12 demonstrated the VERSANT® CT/GC DNA 1.0 assay performed with 99.4% and 99.2% of specificity for N gonorrhoeae and C trachomatis detection, respectively, whereas sensitivity was 100% both for C trachomatis and N gonorrhoeae. As a comparator,
culture methods were 100% specific, but far less sensitive. As a clinical consideration, patients accept antibiotic treatment before their infection status has been confirmed.
Respiratory Viral Panel
A broad spectrum of pathogens is causative for respiratory tract infections, but symptoms are mostly similar. The identification of the causative viruses is only feasible using multiplex PCR or several monoplex PCR tests in parallel. Several studies of various respiratory viral panels,55-57 demonstrate the
multiplex assay detected clinically important viral infections in a single genomic test and thus, may be useful for detecting causative agents for respiratory tract disorders. A 2011 study by Brittain-Long58 on a randomized population of 406 patients with access to a rapid- multiplex-PCR assay used to detect 13
viruses had lower antibiotic prescription rates (4.5% vs 12.3%, respectively) versus delayed identification with no significant difference in outcome at follow-up (p=0.359). Access to a rapid method for etiologic diagnosis of respiratory tract infections may reduce antibiotic prescription rates at the initial visit in an
outpatient setting. Rapid identification of influenza may also lead to more effective early treatment with antivirals and more effective infection control measures.
Staphylococcus aureus and Methicillin-Resistant Staphylococcus aureus
Probes are available for the detection of Staphylococcus aureus.59,60 These probes are able to not only distinguish between coagulase-negative Staphylococcus and S aureus, they can also detect methicillinresistant species (MRSA) with high accuracy.25,26 Given the importance of establishing an early and
accurate diagnosis in clinical situations in which an S aureus infection is likely and there is substantial likelihood of MRSA, testing may be considered medically necessary in these situations. Probes are also available for the detection of enterovirus, although the clinical applicability of these probes has not been
Streptococcus, Group A
Confirmation of the diagnosis of streptococcus A is typically based on culture. However a direct DNA probe test for streptococcus A, using a throat swab, has been used as an alternative to culture, with the advantage of a 45-minute turnaround, compared with several days for culture. The summary of clinical studies included in the product label indicates a 97.4% agreement with confirmatory culture.61 Furthermore, a recent study62 of a laboratory-developed internally controlled rapid Group A streptococcus (GAS) PCR assay using flocked swab throat specimens compared the GAS PCR assay with GAS culture
results using a collection of archived throat swab samples obtained during a study comparing the performance of conventional and flocked throat swabs. The sensitivity of the GAS PCR assay as compared with the reference standard was 96.0% (95% confidence interval [CI], 90.1% to 98.4%), specificity 98.6% (95% CI, 95.8% to 99.5%), PPV 96.9% (95% CI, 91.4% to 99.0%) and NPV of 98.1% (95% CI, 95.2% to 99.2%). For conventional swab cultures, sensitivity was 96.0% (95% CI, 90.1% to 98.4%), specificity 100% (95% CI, 98.2% to 100%), PPV 100%, (95% CI, 96.1% to 100%) and NPV 98.1% (95% CI, 95.2% to 99.3%). The GAS PCR assay appeared to perform as well as conventional throat swab culture, the current standard of practice. Recently, a GAS DNA amplification assay has become available. Sensitivities and specificities of the GAS DNA amplification assay have been reported to be 99% to 100%.63,64 Because the GAS PCR and amplification assay, including DNA extraction, can be performed in approximately 1 hour, prospective studies of this assay are warranted to evaluate the clinical impact of the assay on management of patients with pharyngitis.
Streptococcus, Group B
Several different rapid PCR-based tests for Group B streptococcus (GBS) have been developed, with reported sensitivities and specificities similar to that of conventional culture. DNA probes have also been developed to identify GBS from cultured specimens.65,66
Nye et al67 compared the performance characteristics of PCR testing for trichomonas with wet prep microscopy and culture in 296 female and 298 male subjects. In both women and men, DNA probe testing of vaginal swabs was more sensitive than culture. However, in men, wet prep testing was more
sensitive than DNA probe testing. Munson et al68 compared DNA probe testing and culture in 255 vaginal saline preparations. The DNA probe identified trichomonas in 9.4% (24/255) of specimens that were negative on culture. This probe offers the ability to better distinguish between causes of vaginitis, which
can be difficult clinically and using standard culture methods. Nucleic acid amplification tests have demonstrated higher clinical sensitivity than culture and wet mount microscopy,67 as well as single-probe nonamplified testing in general. A 2011 prospective multicenter study of 1025 asymptomatic and
symptomatic women found nucleic acid amplification testing had clinical sensitivity of 100% for both vaginal and endocervical swabs while urine specimen sensitivity was 95.2%.69 Specificity levels ranged from 98.9% to 99.6%. Other studies have also reported similar results.70 PCR amplification tests have
higher clinical sensitivity and are considered the standard of care for diagnosing Trichomonas vaginalis when culturing is not an option.
Summary of Evidence
Nucleic acid probes are available for the identification of a wide variety of microorganisms, offering more rapid identification compared with standard cultures. Nucleic acid probes can also be used to quantitate the number of microorganisms present. This technology offers advantages over standard techniques
when rapid identification is clinically important and/or when treatment decisions are based on quantitative results. Using these criteria, nucleic acid probes for numerous microorganisms can be considered medically necessary, as delineated in the policy statement.
Practice Guidelines and Position Statements
No guidelines or statements were identified.
U.S. Preventive Services Task Force Recommendations
Nucleic acid probe testing is not a preventive service.
Medicare National Coverage
There is no national coverage determination (NCD). In the absence of an NCD, coverage decisions are left to the discretion of local Medicare carriers.
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