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MP 2.04.20 Apolipoprotein B in the Risk Assessment and Management of Cardiovascular Disease

Medical Policy
Section
Medicine
 
Original Policy Date
5/31/01
 
Last Review Status/Date
Reviewed with literature search/5:2009
Issue
5:2009
Return 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

Low-density lipoproteins (LDL) have been identified as the major atherogenic lipoproteins and have long been identified by the National Cholesterol Education Project (NCEP) as the primary target of cholesterol- lowering therapy. LDL particles consist of a surface coat composed of phospholipids, free cholesterol, and apolipoproteins, surrounding an inner lipid core composed of cholesterol ester and triglycerides. LDL particles can vary both in size and in cholesterol content, and for a given level of LDL-C, there can be a wide variety of both size and numbers of LDL particles. Traditional lipid risk factors such as LDL-C, while predictive on a population basis, are weaker markers of risk on an individual basis. Only a minority of subjects with elevated LDL and cholesterol levels will develop clinical disease, and up to 50% of cases of coronary artery disease occur in subjects with ‘normal’ levels of total and LDL cholesterol. Thus there is considerable potential to improve the accuracy of current cardiovascular risk prediction models. Recently there has been interest in investigating the concentration of LDL particles and their size particles as an independent risk factor. (Small, dense LDL particles are addressed separately in policy No. 2.04.12.)

 

Two basic techniques are used for measuring LDL particle concentration, the surrogate measurement of apolipoprotein B (apo B) or direct measurement of the number of particles using nuclear magnetic spectroscopy. Apo B is the major protein moiety of all lipoproteins except for high-density lipoprotein (HDL). The most abundant form of apo B, large B or B-100, constitutes the apo B found in low-density lipoproteins (LDL) and very-low-density lipoproteins (VLDL). Since both LDL and VLDL each contain 1 molecule of apolipoprotein B, measurement of apo B reflects the total number of these atherogenic particles, 90% of which are LDL. Nuclear resonance spectroscopy (NMR) is based on the fact that lipoprotein subclasses of different size broadcast distinguishable NMR signals. Thus NMR can quantifiy the number of LDL particles of a specific size (i.e., small dense LDL) and can provide a measurement of the total number of particles. (Use of NMR for measuring LDL particle concentration is addressed in policy No. 2.04.12.)


Policy

Measurement of apolipoprotein B is considered investigational as an adjunct to LDL cholesterol in the risk assessment and management of cardiovascular disease.


Policy Guidelines

There is no specific CPT code for measurement of apolipoprotein B. CPT code 82172 (apolipoprotein, each) might be used.


Benefit Application

BlueCard/National Account Issues

Determination of apo B may be offered as a component of a comprehensive cardiovascular risk assessment offered by reference laboratories. Comprehensive risk assessment may include evaluation of small low-density lipoproteins, subclassification of high-density lipoproteins, evaluation of apolipoprotein E genotype or phenotype, total plasma homocysteine, lipoprotein(a), high-sensitivity C-reactive protein, and homocysteine levels. (These components are addressed separately in policy Nos. 2.04.12 and 2.04.202.04.25 )


Rationale 

Apo B as a predictor of cardiovascular risk

The strongest evidence on the predictive ability of apo B in the general population is derived from large prospective cohort studies and nested case-control studies in unselected populations. A number of these types of studies have been reported and are discussed below.

The Quebec Cardiovascular Study (1) evaluated the ability of levels of apo B and other lipid parameters to predict subsequent coronary artery disease (CAD) events in a prospective cohort study of 2,155 men followed up for 5 years. Elevated levels of apo B were found to be an independent risk factor for ischemic heart disease after adjustment for other lipid parameters (RR 1.40; 95% CI: 1.2 –1.7). In patients with an apo B level of greater than 120 mg/dL, there was a 6.2-fold increase in the risk of cardiovascular events.

The Apolipoprotein-Related Mortality Risk Study (ARMORIS) was another prospective cohort study that followed 175,000 Swedish men and women presenting for routine outpatient care over a mean of 5.5 years. (2) This study found that apo B was an independent predictor of CAD events and was superior to LDL-C in predicting risk, both for the entire cohort and in all subgroups examined. Risk ratios for the highest quartile of apo B levels were 1.76 in men (p <0.0001) and 1.69 in women (p <0.001).

A nested case-control study was performed among the 18,225 male participants between the ages of 40 and 75 in the Health Professionals Follow-up Study (3). The relative risk for the development of coronary heart disease in the highest versus lowest quintiles was greater for apo B (3.01, 95% confidence interval [CI]: 1.81 –5.00) compared to LDL-C (1.81, 95% CI: 1.12 –2.93). In a multivariate model, apo B was an independent predictor of cardiovascular events while LDL-C was not.

A cohort study of 15,632 participants from the Women’s Health Initiative (4) provided similar information in women. In this analysis, the hazard ratio for developing coronary heart disease in the highest versus the lowest quintiles was greater for apo B (2.50, 95% CI: 1.68–3.72) compared to LDL-C (1.62, 1.17 –2.25), after adjustment for traditional cardiovascular risk factors.

The Copenhagen City Heart Study (5) was a prospective cohort study of 9,231 asymptomatic persons from the Danish general population followed for 8 years. Individuals with total apo B levels in the top one-third (top tertile) had a significantly increased relative risk of cardiovascular events compared to patients in the lowest one-third, after controlling for LDL-C and other traditional cardiovascular risk factors (RR 1.4, 95% CI: 1.1 –1.8 for men; RR 1.5, 95% CI: 1.1 –2.1 for women). This study also compared the discriminatory ability of apo B with that of traditional lipid measures, by using the area under the curve (AUC) for classifying cardiovascular events. Total apo B levels had a slightly higher AUC compared to LDL-C (0.58 vs. 0.57), however this difference in AUC was not statistically significant.

At least one large prospective cohort study, the Atherosclerosis Risk in Communities (ARIC) study (6), concluded that apo B did not add additional predictive information above standard lipid measures. The ARIC study followed 12,000 middle-aged individuals free of CAD at baseline for 10 years. While apo B was a strong univariate predictor of risk, it did not add independent predictive value above traditional lipid measures in multivariate models.

The ratio of apo B/apo A-I has also been proposed as a superior measure of the ratio of pro-atherogenic (i.e., “bad”) cholesterol to anti-atherogenic (i.e., “good”) cholesterol. This ratio may be a more accurate measure of this concept, compared to the more common total cholesterol (TC)/HDL ratio. A number of epidemiologic studies have reported that the apo B/apo A-I ratio is superior to other ratios, such as TC/HDL-C, or non-HDL chol/HDL-C. (7,8)

A nested case-control study (9) performed within the larger EPIC-Norfolk (European Prospective Investigation into Cancer and Nutrition-Norfolk) cohort study evaluated the predictive ability of the apo B/apo A-I ratio compared to traditional lipid measures. The EPIC-Norfolk study followed 25,663 patients from Norfolk, UK. The case control substudy enrolled 869 patients who had developed CAD during a mean follow-up of 6 years, and 1,511 control patients without CAD. The apo B/apo A-I ratio was an independent predictor of cardiovascular events after controlling for traditional lipid risk factors and the Framingham risk score (adjusted odds ratio 1.85, 95% CI: 1.15-2.98). The addition of the apo B/apo A-I ratio to the Framingham risk model resulted in a statistically significant improvement in discriminatory ability (AUC 0.594 vs. AUC 0.613, p <001), but this small difference was felt to be of questionable clinical value. The authors also reported that the apo B/apo A-I ratio was no better than total cholesterol/HDL ratio for discriminating between cases and controls (AUC 0.673 vs. 0.670, p =0.38).

However, not all studies have supported the superiority of the apo B/apo A-I ratio over traditional measures. In an analysis of data from the Women’s Health Study (4), the ratio of apo B/apo-AI was not superior as a risk factor for future cardiovascular events (HR 3.01, 95% CI: 2.01–4.50) compared to TC/HDL-C (HR 3.81, 95% CI: 2.47–5.86).

Some studies have tested the use of apo B in a multivariate risk prediction models in which both traditional risk factors and apolipoprotein measures were included as potential predictors. Ridker and co-workers (10) published the Reynolds Risk Score, based on data from 24,558 initially healthy women enrolled in the Women’s Health Study and followed up for a median of 10.2 years. A total of 35 potential predictors of cardiovascular disease were considered as potential predictors, and 2 final prediction models were derived. The first model was the best fitting model statistically, and included both apo B and the apo B/apo A-I ratio as 2 of 9 final predictors. The second model, called the “clinically simplified model,” substituted LDL-C for apo-B and total/HDL cholesterol for apo B/apo A-I. The authors developed this simplified model “for the purpose of clinical application and efficiency,” and justified replacing the apo-B and apo B/apo A-I measures as a result of their high correlation with traditional lipid measures (r =0.87 and 0.80 respectively). Ingelsson and co-workers (11) used data from 3,322 individuals in the Framingham Offspring Study to compare prediction models with traditional lipid measures to models that include apolipoprotein and other nontraditional lipid measures. This study reported that the apo B/apo A-I ratio had similar predictive ability to traditional lipid ratios with respect to model discrimination, calibration, and reclassification. The authors also reported that the apo B/apo A-I ratio did not provide any incremental predictive value over traditional measures.

Apo B as a treatment target for hyperlipidemia

A number of randomized controlled trials of statin therapy have examined the change in apo B on treatment in relation to clinical CAD outcomes, and compared whether apo B is a better predictor of outcomes when compared to LDL-C.

The Air Force/Texas Coronary Atherosclerosis Prevention Study (AFCAPS/TexCAPS) evaluated lipid parameters among 6,605 men and women with average LDL and low HDL cholesterol who were randomized to receive either lovastatin or placebo (12). Baseline LDL and HDL cholesterol as well as levels of apo B were predictive of future coronary events. However, in the treatment group, post-treatment levels of LDL-C and HDL-C were not predictive of subsequent risk, while post-treatment apo-B levels were predictive.

In the LIPID (Long-Term Intervention with Pravastatin in Ischemic Disease) trial (13), the relationship of on-treatment apo B levels to clinical outcomes was examined in 9014 patients randomized to pravastatin or placebo and followed for a mean of 6.1 years. The adjusted hazard ratio for apo B levels (2.10, 95% CI: 1.21 –3.64, p =0.008) was higher than that for LDL-C (1.20, 95% CI: 1.00 –1.45, p =0.05). Also, the proportion of the treatment effect explained by on-treatment apo B levels (67%) was higher than that for LDL-C levels (52%).

Kastelein et al. (14) combined data from 2 randomized controlled trials, the TNT (Treating to New Targets) and IDEAL (Incremental Decrease in End Points through Aggressive Lipid Lowering) trials, in order to compare the relationship between response to lipids, apo B levels and other lipid measures. This analysis included 18,889 patients with established coronary disease randomized to low- or high-dose statin treatment. In pairwise comparisons, the on-treatment apo B level was a significant predictor of cardiovascular events (HR 1.24; 95% CI 1.13 –1.36, p <0.001), while LDL level was not. Similarly, the ratio of apo B/apo A-I was a significant predictor of events (HR 1.24; 95% CI: 1.17 –1.32) while the total/HDL cholesterol was not.

Current treatment guidelines

The ATP-III guidelines (15) identify apo B as an “emerging risk factor.” The document notes that to determine their clinical significance, the emerging risk factors must be evaluated against the following criteria:

  • Significant predictive power that is independent of other major risk factors
  • A relatively high prevalence in the population (justifying routine measurement in risk assessment)
  • Laboratory or clinical measurement must be widely available, well standardized, inexpensive, have accepted population reference values, and be relatively stable biologically
  • Preferable, but not necessarily, modification of the risk factor in clinical trials will have shown reduction in risk.

In their discussion of apo B, the guidelines state that the apo B level typically is disproportionately higher in persons with hypertriglyceridemia, and that “ATP III takes this difference into account and sets a secondary target, non HDL cholesterol, in persons with hypertriglyceridemia. Non HDL cholesterol is significantly correlated with apolipoprotein B and can serve as a ‘surrogate’ for it. The non-HDL cholesterol measure is readily available in clinical practice, whereas standardized apolipoprotein B measures are not widely available.”

In 2004, the American College of Physicians published clinical practice guidelines regarding lipid control in the management of type 2 diabetes (16). These guidelines do not address the role of measurement of either apo-B or direct measurements of lipid particle concentration. In July 2004, Grundy and colleagues published an article outlining the implications of recent clinical trials of statin therapy (17). The authors recommended a further lowering of the target LDL-C for some populations of patients. For example, the LDL-C target of 100 mg/dL in high-risk patients was lowered to 70 mg/dL, and the target in moderately high-risk patients was lowered from 130 to 100. In addition, the authors recommended that consideration be given to combining a fibrate or nicotinic acid with an LDL-lowering drug in patients with high triglycerides or low HDL-C concentration. While not an explicit update of the ATP III recommendations, the conclusions were endorsed by the National Heart, Lung, and Blood Institute, the American College of Cardiology Foundation, and the American Heart Association. These new more aggressive targets of therapy create additional questions of how measurements of apo B can be used to improve patient management.

A publication from a recent consensus conference (18) included specific recommendations for incorporating apo B testing into clinical care for high-risk patients. This expert panel stated that “ApoB and LDL particle number also appear to be more discriminating measures of the adequacy of LDL lowering therapy than are LDL cholesterol or non-HDL cholesterol.” They therefore recommend that for patients with metabolic syndrome who are being treated with statins, both LDL cholesterol and apo B should be used as treatment targets, with an apo B target of less than 90 mg/dL. Treatment should be intensified for patients with apo B above this level even if target LDL has been achieved.

A Canadian task force has also endorsed use of apo B as a treatment target, and proposed a target apo B level of 90 mg/dL (19). Other experts have recommended using a lower target of 80 mg/dL for apo B. (20) However, none of the major guideline bodies in the U.S., such as National Cholesterol Education Adult Treatment Panel III (NCEP ATP III), have incorporated apo B targets as part of their formal recommendations.

Conclusions

The evidence suggests that apo B provides independent information on risk assessment for cardiovascular disease and that apo B is superior to LDL-C in predicting cardiovascular risk. Numerous large prospective cohort studies and nested case-control studies have compared these measures and most have concluded that apo B is a better predictor of cardiac risk when compared to LDL-C. There is greater uncertainty around the degree of improvement in risk prediction and whether the magnitude of improvement is clinically significant. While there have been attempts to incorporate apo B into multivariate risk prediction models, at the present time apo B is not included in the models that are most commonly used in routine clinical care, such as the Framingham risk model and the PROCAM (Prospective Cardiovascular Munster Study) Score.

Furthermore, as a marker of response to cholesterol-lowering treatment, apo B may be more accurate than LDL-C, and may provide a better measure of the adequacy of anti-lipid therapy than does LDL-C. Post-hoc analyses of randomized, controlled trials of statin treatment have reported that on-treatment levels of apo B are more highly correlated with clinical outcomes than standard lipid measures. Whether the degree of improvement in assessing treatment response is clinically significant has yet to be determined.

Some experts currently believe that the evidence is sufficient to warrant the routine clinical use of apo B levels as a replacement for LDL-C levels, and the use of the apo B/apo A-I ratio as a replacement for the TC/HDL-C ratio. These experts argue that the use of apo B in place of LDL-C will allow better targeting of anti-lipid therapy, and avoid under-treatment in a substantial number of patients with low or normal LDL levels and small, dense subtype (high apo B). As of the current time, none of the major guidelines, such as NCEP ATP III, have yet to formally incorporate the measurement of apo B into their recommendations.

However, it is not yet possible to conclude that the use of apo B levels will improve outcomes when used in routine clinical care. Improved ability to predict risk and/or treatment response does not by itself result in better health outcomes. (21,22) To improve outcomes, clinicians must have the tools to translate this information into clinical practice. No studies have demonstrated improved health outcomes by using apo B in place of LDL-C for either risk assessment and/or treatment response. The most widely used risk assessment models, such as the Framingham prediction model, and the most widely used treatment guidelines, the ATP III guidelines, do not provide the tools necessary for clinicians to incorporate apo B measurements into routine assessment and management of hyperlipidemic patients. This creates difficulties in interpreting and applying the results of apo B and/or apo B/apo A-I measurements to routine clinical care.

Therefore, the currently available evidence is not sufficient to prompt reconsideration of the policy statement, which remains unchanged.

 

 

References:

  1. Lamarche B, Moorjani S, Lupien PJ et al. Apolipoprotein A-I and B levels and the risk of ischemic heart disease during a five-year follow-up of men in the Quebec cardiovascular study. Circulation 1996; 94(3):273-8.
  2. Walldius G, Jungner I, Holme I et al.High apolipoprotein B, low apolipoprotein A-I, and improvement in the prediction of fatal myocardial infarction (AMORIS study): a prospective study. Lancet 2001; 358(9298);2026-33.
  3. Pischon T, Girman CJ, Sacks FM et al. Non-high density lipoprotein cholesterol and apolipoprotein B in the prediction of coronary heart disease in men. Circulation 2005; 112(22):3375-83.
  4. Ridker PM, Rifai N, Cook NR et al. Non-HDL cholesterol, apolipoproteins A-I and B100, standard lipid measures, lipid ratios, and CRP as risk factors for cardiovascular disease in women. JAMA 2005; 294(3):326-33.
  5. Benn M, Nordestgaard BG, Jensen GB et al. Improving prediction of ischemic cardiovascular disease in the general population using apolipoprotein B: the Copenhagen City Heart Study. Arterioscler Thromb Vasc Biol 2007; 27(3):661-70.
  6. Sharrett AR, Ballantyne CM, Coady SA et al. Coronary heart disease prediction from lipoprotein cholesterol levels, triglycerides, lipoprotein(a), apolipoproteins A-I and B, and HDL subfractions: the Atherosclerosis Risk in Communities (ARIC) Study. Circulation 2001; 104(10):1108-13.
  7. Walldius G, Jungner I. Apolipoprotein B and apolipoprotein A-1: risk indicators of coronary heart disease and targets for lipid modifying therapy. J Intern Med 2004; 255(2):188-205.
  8. Rasouli M, Kiasari AM, Mokhberi V. The ratio of apoB/apoAI, apoB and lipoprotein(a) are the best predictors of stable coronary artery disease. Clin Chem Lab Med 2006; 44(8):1015-21.
  9. van der Steeg WA, Boekholdt SM, Stein EA et al. Role of the apolipoprotein B-apolipoprotein A-I ratio in cardiovascular risk assessment: a case-control analysis in EPIC-Norfolk. Ann Intern Med 2007; 146(9):640-8.
  10. Ridker PM, Buring JE, Rifai N et al. Development and validation of improved algorithms for the assessment of global cardiovascular risk in women: the Reynolds Risk Score. JAMA 2007; 297(6):611-9.
  11. Ingelsson E, Schaefer EJ, Contois JH et al. Clinical utility of different lipid measures for prediction of coronary heart disease in men and women. JAMA 2007; 298(7):776-85.
  12. Gotto AM, Whitney E, Stein EA et al. Relation between baseline and on-treatment lipid parameters and first acute major coronary events in the Air Force/Texas Coronary Atherosclerosis Prevention Study (AFCAPS/TexCAPS). Circulation 2000; 101(5):477-84.
  13. Simes RJ, Marschner IC, Hunt D et al. Relationship between lipid levels and clinical outcomes in the Long-Term Intervention with Pravastatin in Ischemic Disease (LIPID) trial: to what extent is the reduction in coronary events with pravastatin explained by on-study lipid levels? Circulation 2002; 105(10):1162-9.
  14. Kastelein JJ, van der Steeg WA, Holme I et al. Lipids, apolipoproteins, and their ratios in relation to cardiovascular events with statin treatment. Circulation 2008; 117(23):3002-9.
  15. Expert Panel on Detection, Evaluation and Treatment of High Blood Cholesterol in Adults. Executive summary of the third report of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III). JAMA 2001; 285(19):2486-97.
  16. Snow V, Aronson MD, Hornbake ER et al. Lipid control in the management of type 2 diabetes mellitus: a Clinical Practice Guideline from the American College of Physicians. Ann Intern Med 2004; 140(8):644-9.
  17. Grundy SM, Cleeman JI, Merz CN et al. Implications of recent clinical trials for the National Cholesterol Education Program Adult Treatment Panel III guidelines. Circulation 2004; 110(2):227-39.
  18. Brunzell JD, Davidson M, Furberg CD et al. Lipoprotein management in patients with cardiometabolic risk: consensus statement from the American Diabetes Association and the American College of Cardiology Foundation. Diabetes Care 2008; 31(4):811-22.
  19. Genest J, Frohlich J, Fodor G et al. Recommendations for the management of dyslipidemia and the prevention of cardiovascular disease: summary of the 2003 update. CMAJ 2003; 169(9):921-4.
  20. Barter PJ, Ballantyne CM, Carmena R et al. Apo B versus cholesterol in estimating cardiovascular risk and in guiding therapy: report of the thirty-person/ten-country panel. J Intern Med 2006; 259(3):247-58.
  21. 2002 TEC Assessments; Tab 23 (Special Report)
  22. Ware JH. The limitations of risk factors as prognostic tools. N Engl J Med 2006; 355(25):2615-7.
  23. Mudd JO, Borlaug BA, Johnston PV et al. Beyond low-density lipoprotein cholesterol: defining the role of low-density lipoprotein heterogeneity in coronary artery disease. J Am Coll Cardiol 2007; 50(18):1735-41.

 

 

Codes

Number

Description

CPT 

82172 

Apolipoprotein, each 

ICD-9 Procedure 

 

 

ICD-9 Diagnosis 

250 

Diabetes, code range 

 

272 

Disorders of lipid metabolism, code range 

 

410–414 

Ischemic heart disease code range 

 

440 

Atherosclerosis, code range 

 

443 

Peripheral vascular disease, code range 

 

V12.5 

Personal history of disease of the circulatory system 

 

V17.3-17.4 

Family history of ischemic heart disease or other cardiovascular disease, respectively 

HCPCS 

 

 

Type of Service 

Pathology/Laboratory 

Place of Service 

Outpatient 


Index

Apolipoprotein B
Cardiovascular Risk Assessment, Apolipoprotein B


Policy History

Date Action Reason
05/31/01 Add to Medicine section New policy
04/29/03 Replace policy Policy updated; no change in policy statement, references added
11/9/04 Replace policy Policy updated; no change in policy statement, references added
08/17/05 Replace policy Policy updated; no change in policy statement, references 12 and 13 added
02/15/07 Replace policy Policy updated with literature search through December 2006; no change in policy statement. Reference numbers 4–9, 14–16, and 19 added and other references renumbered 
04/09/08 Replace policy  Policy updated with literature search from January 2007 through March 2008; references 22 through 31 added. Policy statement unchanged
05/14/09 Replace policy Policy extensively revised with literature search; previous updates condensed. References condensed and reordered; reference numbers 13, 14, and 18 added. No change to policy statement.


 

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