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MP 7.01.71 Lung Volume Reduction Surgery for Severe Emphysema

Medical Policy    
Section
Surgery 
Original Policy Date
7/16/99
Last Review Status/Date
Reviewed with literature search/6:2014
Issue
6:2014
  eturn to Medical Policy Index

Disclaimer

Our medical policies are designed for informational purposes only and are not an authorization, or an explanation of benefits, or a contract.  Receipt of benefits is subject to satisfaction of all terms and conditions of the coverage.  Medical technology is constantly changing, and we reserve the right to review and update our policies periodically.


Description

Lung volume reduction surgery (LVRS) is proposed as a treatment option for patients with severe emphysema who have failed optimal medical management. The procedure involves the excision of diseased lung tissue and aims to reduce symptoms and improve quality of life.

Background

Lung volume reduction is a surgical treatment for patients with severe emphysema involving the excision of peripheral emphysematous lung tissue, generally from both upper lobes. The precise mechanism of clinical improvement for patients undergoing lung reduction surgery has not been firmly established. However, it is believed that elastic recoil and diaphragmatic function are improved by reducing the volume of diseased lung. In addition to changes in chest wall and respiratory mechanics, the surgery is purported to correct ventilation perfusion mismatch and improve right ventricular filling.

Research on LVRS has focused on defining the subgroup of patients most likely to benefit from the procedure. Potential benefits of the procedure eg, improvement in functional capacity and quality of life must be weighed against the potential risk of the procedure eg, risk of postoperative mortality.

Regulatory Status

Not applicable.


Policy

Lung volume reduction surgery (LVRS) as a treatment for emphysema may be considered medically necessary in patients with emphysema who meet ALL of the following criteria*:

  • Predominantly upper lobe emphysema with hyperinflation and heterogeneity (ie, target areas for removal)
  • Forced expiratory volume in 1 second (FEV1):
    • For patients who are younger than 70 years of age, the FEV1 must be no more than 45% of the predicted value.
    • For patients who are 70 years of age or older, the FEV1 must be no more than 45% of the predicted value and 15% or more of the predicted value.
  • Marked restriction in activities of daily living, despite maximal medical therapy
  • Age younger than 75 years
  • Acceptable nutrition status; ie, 70% to 130% of ideal body weight
  • Ability to participate in a vigorous pulmonary rehabilitation program
  • No coexisting major medical problems that would significantly increase operative risk
  • Willingness to undertake risk of morbidity and mortality associated with LVRS
  • Abstinence from cigarette smoking for at least 4 months

Lung volume reduction surgery is considered investigational in all other patients.

* Patient selection criteria are based on the National Emphysema Treatment Trial (NETT).


Policy Guidelines

The following additional criteria, also from the NETT trial, may provide further information in determining whether a patient is a candidate for LVRS:

  • Pao2 on room air 45 mm Hg or more (30 mm Hg or more at elevations of 5000 feet or higher)
  • Paco2 on room air less than or equal to 60 mm Hg (less than or equal to 55 mm Hg at elevations of 5000 feet or higher)
  • Postrehabilitation 6-minute walk of at least 140 meters, and able to complete 3 minutes of unloaded pedaling in exercise tolerance test

CPT code 32491 explicitly describes lung volume reduction surgery.

In 2012, a new code 32672 was added for thoracoscopic lung volume reduction surgery. The code is a unilateral code but the procedure should be performed bilaterally to accomplish a true lung volume reduction surgery.

In 2004, the following HCPCS codes were introduced that describe pre- and postoperative services related to LVRS:

G0302: Preoperative pulmonary surgery services for preparation for LVRS, complete course of services to include a minimum of 16 days of services

G0303: Preoperative pulmonary services for preparation for LVRS, 10 to 15 days of services

G0304: Preoperative pulmonary surgery services for preparation for LVRS, 1 to 9 days

G0305: Post-discharge pulmonary surgery services after LVRS, minimum of 6 days of services

 

Benefit Application
BlueCard/National Account Issues

Lung volume reduction surgery is a complex procedure, and reduplication of the positive results reported in the National Emphysema Treatment Trial (NETT) may only be achieved by institutions experienced in this surgery.


Rationale

The policy was created in 1999 with a search of the MEDLINE database. The policy was on "no further review" status from 2005 to 2010 following the 2003 publication of the National Emphysema Treatment Trial (NETT) findings. In 2010, the policy returned to active review and was updated regularly with MEDLINE searches. The most recent literature review was conducted through May 10, 2014. Following is a summary of the key published literature to date:

National Emphysema Treatment Trial

NETT was a large multicenter prospective randomized controlled trial (RCT) comparing lung volume reduction surgery (LVRS) with optimal medical therapy. Two-year findings were published in 2003 by Fishman et al.(1) The trial included 1218 patients, and the analysis was intention to treat, reporting on of all randomized patients. The primary outcomes included total 30-day, and 90-day mortality and maximal exercise capacity. Secondary outcomes included pulmonary function, the distance walked in 6 minutes, and self-reported health-related quality of life and general quality of life. At the time of data analysis, 371 (30%) patients had been followed up for a total of 24 months. Primary findings of the Fishman et al study are summarized in Table 1.

Table 1.

 

90-Day Mortality, %

Total Mortality (No. Death/Total)

Improvement in

Exercise Capacity at 24 Months, %b

Improvement in Quality of Life at 24 Months, %c

 

Med Tx

Surg Tx

Med Tx

Surg Tx

Med Tx

Surg Tx

Med Tx

Surg Tx

All patients

1.3

7.9

160/610

157/608

3

15

9

33

High-risk patientsa

28

0

30/70

42/70

2

7

0

10

Upper-lobe emphysema with low exercise capacity

3.3

2.9

51/151

26/139

0

30

10

48

Upper-lobe emphysema with high exercise capacity

0.9

2.9

39/213

34/206

3

15

11

41

Non-upper-lobe emphysema, low exercise capacity

0

8.3

28/84

26/65

7

12

7

37

Non-upper-lobe emphysema, high exercise capacity

0.9

10.1

27/109

14/111

3

3

12

15

a High risk is defined as those with a forced expiratory volume in 1 second that was ≤20% of the predicted value and either homogeneous emphysema on computed tomography or a carbon monoxide diffusion capacity that was ≤20% of the predicted value.

b Improvement in exercise capacity in patients followed up for 24 months after randomization was defined as an increase in the maximal workload of >10 W from the patient’s postrehabilitation baseline value.

c Improvement in health-related quality of life in patients followed up for 24 months after randomization was defined as a decrease in the score on the St George’s Respiratory Questionnaire of >8 points (on a 100-point scale) from the patient’s postrehabilitation baseline score.

Conclusions drawn from these data include:

  • Overall, LVRS increased the chance of improved exercise capacity but did not confer a survival advantage over medical therapy.
  • There was a survival benefit for those patients who had both predominantly upper lobe emphysema and low baseline exercise capacity. This survival advantage appears to be due to the very high mortality and marked progressive functional limitation of those treated medically.
  • Patients considered at high risk and those with non-upper lobe emphysema and high baseline exercise capacity were found to be poor candidates for LVRS.

In 2006, a follow-up analysis of data from NETT was published; there was a median follow-up of 4.3 years compared with 2.4 years in the initial full report.(2) Seventy percent of randomized patients participated in the extension of follow-up conducted in 2003, and 76% participated in the mailed quality-of-life data collection in 2004. The analysis was done on an intention-to-treat basis including all 1218 randomized patients. Median follow-up was 4.3 years.

Overall, LVRS showed a mortality benefit compared with medical therapy. During follow-up, 46.5% (283/608) patients in the LVRS group and 53.1% (324/610) patients in the medical therapy group died (relative risk [RR], 0.85, p=0.02). However, the long-term mortality benefit was limited to the subgroup of participants who had predominately upper lobe emphysema and low exercise capacity (those found in the initial report to benefit from LVRS) (RR=0.57, p=0.01). Moreover, in this subgroup of patients (n=290), compared with medical therapy, those in the LVRS group were also more likely to have an improvement in exercise capacity throughout 3 years of follow-up testing (p<0.01) and to have an 8-point improvement in quality of life through 4-year follow-up testing (p=0.003).

In the subgroup of patients with predominately upper lobe emphysema and high exercise capacity (n=419), there was not a survival benefit associated with LVRS, but there was a significantly higher improvement in exercise capacity over 3 years (p<0.001) and quality of life over 4 years (p=0.003 in year 4). Patients with non-upper-lobe emphysema, and either high or low exercise capacity, did not significantly benefit from surgery in terms of mortality rates, exercise capacity, or quality of life. A limitation of the long-term follow-up study was that fewer than 80% of surviving NETT participants took part in the study extension.

In 2010, Sanchez et al published an analysis of data from the NETT further examining factors associated with a positive outcome after LVRS.(3) The analysis focused on patients with upper lobe predominance and a heterogeneous distribution of emphysema defined as a difference in severity of emphysema in any 2 zones of the lung of at least 2 points on a 0-to-4 severity scale. Of the 1218 patients enrolled in the study, 511 patients (42%) met both of these criteria; 261 were in the LVRS group, and 250 were in the medical therapy group, Using Kaplan-Meier analysis, the 3-year survival rate was 81% in patients receiving LVRS and 74% for those the medical group (p=0.05). At 5 years, the estimated survival rate was significantly higher in the LVRS group than the medical therapy group, 70% versus 60% (p=0.02). Maximal exercise capacity, another NETT primary outcome, was a mean of 49 watts in the LVRS group and 38 watts in the medical therapy group at 1 year (p<0.001). At 3 years, the values in the 2 groups were 43 and 38 watts, respectively, and the between-group difference was not statistically significant.

Additional RCTs evaluating LVRS for treating emphysema have been published, and 2 meta-analyses of RCTs have been published.(4,5) Each meta-analysis included 8 RCTs published between 1999 and 2006. However, NETT accounted for about 75% of the patients in both meta-analyses, limiting the usefulness of the findings of the pooled analyses. In the more recent meta-analysis, pooled analyses found a significantly higher odds of mortality in the medical therapy group compared with LVRS at 3 months (odds ratio [OR], 5.16; 95% confidence interval [CI], 2.84 to 9.35) and no statistically significant difference between groups in mortality at 12 months (OR=1.05; 95% CI, 0.82 to 1.33).(5) The authors did not conduct subgroup analyses eg, by location of emphysema, exercise capacity, or heterogeneity of emphysema.

Selected RCTs (other than NETT) are summarized next.

Hillerdal et al conducted a multicenter study in Sweden evaluating LVRS that was published in 2005.(6) Eligibility criteria included age 75 years or younger, FEV-1 of no more than 35% of predicted normal value; excessive hyperinflation with a residual volume of at least 200% of predicted, with radiologic signs of emphysema and decreased mobility of the diaphragm. Participants were required to successfully complete a 6-week physical training program. Of the 114 patients eligible for the initial training (of 304 evaluated), 3 were unable to complete the program, and 5 died before completion; the remaining 106 patients were randomized to continued physical training alone (n=53) or LVRS plus continued physical training for 3 months postsurgery (n=53). A total of 42 (79%) patients in the surgery group and 43 (81%) in the physical training group were followed for 1 year; intention-to-treat analysis was used. The primary outcome was health status according to the Swedish version of the 36-Item Short-Form Health Survey (SF-36) and the disease-specific St. George’s Respiratory Questionnaire (SGRQ). Both instruments have scores ranging from 0 to 100; in the SF-36, 100 represents the best health status and in the SGRQ, 100 represents poor health status. For both instruments, the minimally important clinical difference was defined as 4 scale points. In an analysis adjusting for age and sex, there was a significant difference in the score on the SGRQ at 6 months (mean difference, 14.3 points) and 12 months (mean difference, 14.7 points), favoring the LVRS group. The total score on the SF-36 at follow-up was not reported. At 12 months, there was significantly more improvement in 6 of the 8 SF-36 subscales in the LVRS group compared with the physical training group. The researchers only reported mean difference in the scales, not the proportion of patients who achieved a certain level of improvement. Mortality was a secondary outcome. There were 7 deaths in the LVRS group (13%) and 2 deaths in the physical training group (4%); this difference was not statistically significant (p=0.5), but the study was likely underpowered for this outcome. Six of the deaths in the LVRS group were caused by respiratory failure and pneumonia; the seventh patient died suddenly at home. Respiratory failure was also the cause of the 2 deaths in the physical training group. The authors point out that the baseline SGRQ scores were lower than in the NETT (59 vs 53, respectively), suggesting a more severely impaired population. The study did not examine patient outcomes according to upper-lobe predominance or initial exercise capacity.

In 2006, Miller et al published a study with data from 5 centers in Canada (Canadian Lung Volume Reduction Surgery [CLVRS] trial).(7) Eligibility criteria included: age between 40 and 79 years; disabling dyspnea; FEV1 of no more than 40% of predicted; diffusing capacity no more than 60%; and total lung capacity no more than 120% or residual volume no less than 200%. After eligibility screening, medical therapy was optimized, and patients were randomized to LVRS (n=32) or continued medical therapy (n=30). The researchers had originally planned to enroll 350subjects, but due to the low proportion of screened subjects who were eligible, they stopped recruitment when only 18% of their target was met (467 people were screened to identify 62 who were eligible). Thus, the study may have been underpowered to detect differences in outcomes between groups. None of the randomized patients were lost to follow-up, and analysis was intention to treat. The overall 2-year survival rate was similar in the 2 groups; there were 5 of 32 (16%) deaths in the LVRS group and 4 of 30 (13%) deaths in the medical therapy group (p=0.935). At 3 and 6 months, there was a significantly higher change from baseline in FEV1 in the LVRS group compared with the medical therapy group, but there was a nonsignificant difference between groups in FEV1 at 12 and 24 months. The mean difference in FEV1 at 24 months was 0.06 liters.

In 2013, Agzarian et al published long-term results of the CLVRS trial.(8) Fifty-two of 62 randomized patients (84%) were available for the long-term follow-up 8 to 10 years after treatment. One patient was excluded before surgery and 9 others were lost to follow-up. The proportion of patients surviving 5 and 10 years was 46% and 7%, respectively, in the LVRS group and 25% and 0% in the control group. According to Kaplan-Meier survival analysis, median survival was 63 months in the LVRS group and 47 months in the control group; the difference between groups was not statistically significant (p=0.20).

Observational studies

Representative larger observational studies are described below.

In 2012, Baldi et al conducted a retrospective analysis that included longer term follow-up than had been reported in the RCTs. The study included 52 emphysema patients who had LVRSs between 1993 and 2000.(9) The 5-year survival rate was 73%, and the 12-year survival rate was 20%. Eleven of 52 patients (21%) underwent lung transplantation a mean of 52 months after LVRS. In a multivariate model, 2 variables were statistically associated with patient survival. These were preoperative pulmonary arterial pressure (hazard ratio [HR], 2.11; 95% CI, 0.99 to 4.45) and upper lobe distribution of emphysema (HR=2.43; 95% CI, 1.10 to 5.36).

In 2014, Decker et al reviewed data on 538 patients from the Society of Thoracic Surgeons (STS) Database who received LVRS, and compared these data with those of the 608 NETT participants randomized to the surgery group.(10) None of the patients in the STS database had an FEV1 less than 20% of predicted or a carbon monoxide diffusing capacity less than 20% of predicted; thus, these patients would not have been considered high risk in NETT. However, about 10% of patients in the STS database had previous cardiothoracic surgery and 1.5% had lung cancer, and these would have been exclusion criteria in NETT. Overall, the mortality rate within 30 days of LVRS was not significantly different in the STS database compared with NETT (5.6% vs 3.6%, p=0.113). When database findings were compared with non-high-risk NETT participants, the 30-day mortality rate was significantly higher among patients in the STS database than NETT patients (5.6% vs 2.2%, p=0.005). This study was descriptive and did not attempt to propose patient selection criteria for LVRS.

Summary

Findings from the National Emphysema Treatment Trial (NETT), a multicenter randomized controlled trial (RCT), suggest that lung volume reduction surgery (LVRS) is effective at reducing mortality and improving quality of life in selected patients with severe emphysema. In subgroup analysis, LVRS offered a survival advantage only in the group of patients not considered high risk who had predominately upper lobe emphysema and low initial exercise capacity. Moreover, patients with upper lobe emphysema, regardless of initial exercise capacity, experienced significant improvement in exercise capacity and quality of life after LVRS. Other, smaller RCTs generally had similar findings though they tended to be underpowered for some outcomes and did not stratify by distribution of emphysema. For the subgroup of patients with predominately non-upper lobe emphysema, NETT did not find significant mortality advantages or symptom improvement with LVRS. Although NETT had positive findings for the study population as a whole, given the risks involved in surgery, additional data are needed to confirm the net health outcome in patients with non-upper lobe emphysema. Therefore, LVRS is considered medically necessary in patients with predominately upper lobe emphysema who are otherwise similar to NETT participants and investigational for other patients.

Practice Guidelines and Position Statements

The American Thoracic Society issued a statement on LVRS in 1996.(11) This was before publication of NETT findings; at the time, the society stated that LVRS appeared to be helpful in some, but not all, patients with advanced emphysema. As of April 2014, this statement is archived and had not been updated.

Medicare National Coverage

Effective for services performed on or after January 1, 2004, Medicare considers LVRS reasonable and necessary for patients with severe upper lobe predominant emphysema or severe non-upper-lobe emphysema and low exercise capacity who meet all of the following requirements(12):

Table 2.

Assessment

Criteria

History and physical examination

  • Consistent with emphysema
  • Body mass index ≤31.1 kg/m2 (men) or ≤32.3 kg/m2 (women)
  • Stable with ≤20 mg prednisone (or equivalent) daily

Radiographic

  • High-resolution computer tomography scan evidence of bilateral emphysema

Pulmonary function (prerehabilitation)

  • Forced expiratory volume in 1 s ≤45% predicted (≥15% predicted if age ≥70 y)
  • Total lung capacity ≥100% predicted postbronchodilator

    Residual volume ≥150% predicted postbronchodilator

Arterial blood gas level (prerehabilitation)

  • Pco2 ≤60 mm Hg (Pco2 ≤55 mm Hg if 1 mile above sea level)

    Po2 ≥45 mm Hg on room air (Po2 ≥30 mm Hg if 1 mile above sea level)

Cardiac assessment

Approval for surgery by cardiologist if any of the following are present: Unstable angina; LVEF cannot be estimated from the echocardiogram; LVEF <45%; dobutamine-radionuclide cardiac scan indicates coronary artery disease or ventricular dysfunction; arrhythmia (>5 premature ventricular contractions per minute; cardiac rhythm other than sinus; premature ventricular contractions on EKG at rest)

Surgical assessment

  • Approval for surgery by pulmonary physician, thoracic surgeon, and anesthesiologist postrehabilitation

Exercise

  • Postrehabilitation 6-min walk of ≥140 m; able to complete 3 min unloaded pedaling in exercise tolerance test (pre- and postrehabilitation)

Consent

  • Signed consents for screening and rehabilitation

Smoking

  • Plasma cotinine level ≤13.7 ng/mL (or arterial carboxyhemoglobin ≤2.5% if using nicotine products)

    Nonsmoking for 4 mo before initial interview and throughout evaluation for surgery

Preoperative diagnostic and therapeutic program adherence

  • Must complete assessment for and program of preoperative services in preparation for surgery

LVEF: left ventricular ejection fraction; Med: medical; Surg: surgical; Tx: treatment.
There are additional criteria specifying eligible facilities.

References:

  1. Fishman A, Martinez F, Naunheim K et al. A randomized trial comparing lung-volume-reduction surgery with medical therapy for severe emphysema. N Engl J Med 2003; 348(21):2059-73.
  2. Naunheim KS, Wood DE, Mohsenifar Z et al. Long-term follow-up of patients receiving lung-volume-reduction surgery versus medical therapy for severe emphysema by the National Emphysema Treatment Trial Research Group. Ann Thorac Surg 2006; 82(2):431-43.
  3. Sanchez PG, Kucharczuk JC, Su S et al. National Emphysema Treatment Trial redux: accentuating the positive. J Thorac Cardiovasc Surg 2010; 140(3):564-72.
  4. Tiong LU, Davies R, Gibson PG et al. Lung volume reduction surgery for diffuse emphysema. Cochrane Database Syst Rev 2006; (4):CD001001.
  5. Huang W, Wang WR, Deng B et al. Several clinical interests regarding lung volume reduction surgery for severe emphysema: meta-analysis and systematic review of randomized controlled trials. J Cardiothorac Surg 2011; 6:148.
  6. Hillerdal G, Lofdahl CG, Strom K et al. Comparison of lung volume reduction surgery and physical training on health status and physiologic outcomes: a randomized controlled clinical trial. Chest 2005; 128(5):3489-99.
  7. Miller JD, Malthaner RA, Goldsmith CH et al. A randomized clinical trial of lung volume reduction surgery versus best medical care for patients with advanced emphysema: a two-year study from Canada. Ann Thorac Surg 2006; 81(1):314-20; discussion 20-1.
  8. Agzarian J, Miller JD, Kosa SD et al. Long-term survival analysis of the Canadian Lung Volume Reduction Surgery trial. Ann Thorac Surg 2013; 96(4):1217-22.
  9. Baldi S, Oliaro A, Tabbia G et al. Lung volume reduction surgery 10 years later. J Cardiovasc Surg (Torino) 2012; 53(6):809-15.
  10. Decker MR, Leverson GE, Jaoude WA et al. Lung volume reduction surgery since the National Emphysema Treatment Trial: Study of Society of Thoracic Surgeons Database. J Thorac Cardiovasc Surg 2014.
  11. American Thoracic Society. Lung volume reduction surgery. 1996. Available online at: http://www.thoracic.org/statements/resources/archive/lvrs.pdf. Last accessed April, 2014.
  12. Center for Medicare and Medicaid Services. National coverage determination for lung volume reduction surgery (reduction pneumoplasty) (240.1). 2005. Available online at: http://www.cms.gov/medicare-coverage-database/details/ncd-details.aspx?NCDId=119&ncdver=3&CoverageSelection=National&KeyWord=lung+volume+reduction+surgery&KeyWordLookUp=Title&KeyWordSearchType=And&clickon=search&bc=gAAAABAAAAAAAA%3d%3d&. Last accessed April, 2014.
 

Codes

Number

Description

CPT  32491  Removal of lung, other than total pneumonectomy; excision-plication of emphysematous lung(s) (bullous or non-bullous) for lung volume reduction, sternal split or transthoracic approach, with or without any pleural procedure 
  32672 Thoracoscopy, surgical; with resection-plication for emphysematous lung (bullous or non-bullous) for lung volume reduction (LVRS), unilateral includes any pleural procedure, when performed  – Note: the procedure should be performed bilaterally.
HCPCS  G0302  Preoperative pulmonary surgery services for preparation for LVRS, complete course of services to include a minimum of 16 days of services 
  G0303  Preoperative pulmonary services for preparation for LVRS, 10 to 15 days of services 
  G0304  Preoperative pulmonary surgery services for preparation for LVRS, 1 to 9 days 
  G0305  Post-discharge pulmonary surgery services after LVRS, minimum of 6 days of services 
ICD-9 Diagnosis  492.0, 492.8 Emphysema code range
ICD-9 Procedure

32.22

Lung volume reduction surgery
ICD-10-CM (effective 10/1/15) J43.0-J43.9 Emphysema code range
   J44.0 –J44,9 Chronic obstructive pulmonary disease code range (used for emphysema with chronic obstructive bronchitis)
ICD-10-PCS (effective 10/1/15) 0BBC0ZZ Excision, upper lung lobe right, open
   0BBD0ZZ Excision, middle lung lobe right, open
   0BBF0ZZ Excision, lower lung lobe right, open
   0BBG0ZZ Excision, upper lung lobe left, open
   0BBH0ZZ Excision, lung lingula, open
   0BBJ0ZZ Excision, lower lung lobe left, open
   0BBK0ZZ Excision, lung, right, open
   0BBL0ZZ Excision, lung, left, open
   0BBM0ZZ Excision, lungs bilateral, open
Type of Service  Surgery 
Place of Service  Inpatient 


Index

Emphysema, Lung Volume Reduction Surgery
Lung Volume Reduction Surgery, Emphysema


Policy History

Date Action Reason
07/16/99 Add to Surgery section New policy
02/15/02 Replace policy Policy updated; no change in policy statement
12/17/03 Replace policy Policy updated; LVRS now considered medically necessary in certain patients. New HCPCS codes added
4/1/05 Replace policy Policy updated; policy statement unchanged; no further scheduled review
06/10/10 Replace policy Policy updated with literature search; 4 month time-frame added to time for tobacco abstinence, other policy statements unchanged; additional details added to policy guidelines; references 4-9 added.
6/9/11 Replace policy Policy updated with literature search. References 8 and 9 added; FEV-1 criteria in medically necessary statement changed to less than 45% predicted for patients age 70 or younger and greater than 15% predicted for patients over age 70.
06/14/12 Replace policy Policy updated with literature search. Rationale substantially revised. Reference 5 added; other references renumbered or removed. No change in policy statements
6/13/13 Replace policy Policy updated with literature search through April 29, 2013. Reference 8 added; other references renumbered. No change in policy statements.
6/12/14 Replace policy Policy updated with literature review through May 10, 2014. References 8 and 10 added. Policy statements unchanged.