Another substudy from the IRAS study compared ~LDL-C with apoB as a correlate for a variety ofASCVD risk factors, including dyslipidemia, insulin resistance, hypertension, inflammation, thrombosis, and subclinical atherosclerosis (38). This interesting comparison examined differences between a group who had high ~LDL-C but normal apoB (i.e., high cholesterol mass distributed among a normal number of particles) and a group who had normal ~LDL-C but high apoB (i.e., normal cholesterol mass distributed among a larger number of particles). The latter hyper-apoB group had significantly higher TGs, fasting and 2-h insulin, and plasminogen activator inhibitor, and lower HDL-C, LDL particle size, and age than the group with isolated ~LDL-C elevation. This analysis raises the possibility that the normal ~LDL-C in the hyper-apoB group is not reassuring. Because apoB is a measure of particle number, this finding points to a discrepancy between the ~LDL-C and the number of atherogenic particles. Moreover, the magnitude of correlation with a variety of other risk markers was generally greater for apoB than ~LDL-C. Surprisingly, when ~LDL-C was adjusted for apoB, it switched from being a positive correlate with the other risk factors to a negative correlate. However, adjusting apoB for ~LDL-C magnified the strength of apoB as a positive correlate with the other risk factors. Similarly, when both apoB and ~LDL-C were adjusted by the Framingham Risk Score, apoB gained strength as a positive correlate, whereas ~LDL-C was weakened. Although this study was not based on outcomes, it lends credence to the idea that apoB can reveal residual risk associated with lipoproteins beyond ~LDL-C.
A substudy from the Quebec Cardiovascular Study evaluated the concordance and discordance between the different risk markers apoB, ~LDL-C, and non-HDL-C among men without CHD (27). Although apoB and ~LDL-C correlated with each other (p = 0.78; p < 0.001), only half of the subjects were in the same quintiles of each marker (i.e., 50% concordance between the markers). Concordance was below 40% for the middle three quintiles, corresponding with an ~LDL-C between 120 and 180 mg/dL. This reinforces the notion that ~LDL-C is not reliably related to the number of lipoproteins; thus, apoB may provide novel information beyond ~LDL-C.
Was this article helpful?