The Value of Apo B Measurements
Abstract & Commentary
By Michael H. Crawford, MD
Source: Ballantyne CM, et al. Statin therapy alters the relationship between apolipoprotein B and low-density lipoprotein cholesterol and non-high-density lipoprotein cholesterol targets in high-risk patients. The MERCURY II (Measuring Effective Reductions in Cholesterol Using Rosuvastatin) trial. J Am Coll Cardiol. 2008;52:626-632.
In patients with elevated triglycerides, other atherogenic particles may be as important as LDL-cholesterol (C). These particles and LDL-C are measured as non-HDL-C, and are considered a secondary target of therapy. An alternative approach is to measure apolipoprotein B (apo B) concentration; which estimates the total number of atherogenic particles in the blood, and is a powerful predictor of cardiovascular events. However, the relationship of apo B, LDL-C, and non-HDL-C cholesterol on statin therapy is poorly understood. Thus, Ballantyne et al used data from the Measuring Effective Reductions in Cholesterol Using Rosuvastatin therapY (MERCURY) study to study these relationships. MERCURY examined the effects of statin therapy in almost 2,000 patients with high coronary artery disease (CAD) risk; LDL-C > 130 but < 250; and triglycerides < 400 mg/dL. At the end of the trial, 1,802 patients were on atorvastatin (357), rosuvastatin (1082), and simvastatin (363). At the end of 16 weeks, all three agents reduced all three lipid parameters so the data was pooled. The recommended target for apo B of < 90 was about equal to an LDL-C of 100 and a non-HDL-C of 130mg/dL at baseline.
During statin therapy to achieve an apo B < 90 required lowering non-HDL-C to < 100 and LDL-C to < 70mg/dL or < 80 in patients with normal triglycerides. Since non-HDL-C and apo B were highly correlated on statin therapy (r2 = 0.92), non-HDL-C could be substituted for measuring apo B. Ballantyne et al concluded that the more aggressive lipid goals recommended for CAD patients should be recommended for patients at high risk for CAD because their achievement is more likely to result in an apo B level < 90mg/dL.
Commentary
Statins are highly effective at lowering LDL-C, but achieving recommended levels may not adequately reduce all atherogenic particles, as measured by apo B levels. Although LDL-C and non-HDL-C levels are linearly related to apo B levels, the relationship is different on and off statins, such that lower LDL-C and non-HDL-C targets are needed to achieve apo B < 90mg/dL. If you are evaluating a patient on therapy and their LDL-C is < 100, about half will have an apo B < 90, but if their LDL-C is < 70, 86% will have an apo B < 90. Likewise, if non-HDL-C is < 130, half will be at the apo B target, and if non-HDL-C is < 100, 92% will be at the apo B target.
Thus, during therapy, in order to reliably get apo B < 90, the more strict guidelines for LDL-C and non-HDL-C should be used. If one measures apo B on therapy and it is < 90, then about 100% will have an LDL-C < 100, but only 58% will be below 70. Similarly, with an apo B < 90, about 100% will have a non-HDL-C < 130 and 82% will have non-HDL-C < 100. Therefore, to ensure full protection for high-risk patients by lowering apo B to less than 90, the stricter secondary prevention targets for LDL-C and non-HDL-C should be used.
Since this data was derived from a pharmaceutical trial, only patients with high lipid values were selected. In fact, none of the patients had an apo B < 90, LDL-C < 100, or a non-HDL-C < 130. Therefore, estimations of the relationship between these lipid parameters in the low ranges are extrapolated, but there is no actual data to confirm the findings. The data suggest that if your LDL-C is < 100 off therapy your apo B is < 90. Also, if your non-HDL-C is < 130 your apo B is < 90. However, actual data in normal controls will be needed to confirm this. Thus, in patients with LDL-C and non-HDL-C levels below targets, yet with evidence of CAD, it would still be worth measuring apo B, Lp (a), and perhaps other lipid fractions. Interestingly, the relationship between LDL-C, non-HDL-C, and apo B was not affected by sex or the presence of diabetes in this study.
In patients with elevated triglycerides, other atherogenic particles may be as important as LDL-cholesterol (C). These particles and LDL-C are measured as non-HDL-C, and are considered a secondary target of therapy.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
- Award-winning Medical Content
- Latest Advances & Development in Medicine
- Unbiased Content