Non-HDL-cholesterol as valid surrogate to apolipoprotein B100 measurement in diabetes: Discriminant Ratio and unbiased equivalence

Abstract

Background: Apolipoprotein B100 (apoB) is a superior indicator of CV risk than total or LDL-C. Non-HDL-C represents a simple surrogate for apoB in hypertriglyceridemic and/or T2DM patients. ApoB and non-HDL-C show high correlation, although the degree of mutual concordance remains debated in CV risk evaluation.

Objectives: We used the Discriminant Ratio (DR) methodology to compare the performance of non-HDL-C with that of apoB to rank diabetic patients according to dyslipidemia and to establish the underlying relationship between these variables taking measurement noise and intra-/intersubject variation into account, and to derive an unbiased equivalence equation.

Methods: Fasting total C, HDL-C, apoB and triglycerides were measured in 45 diabetic patients. The DR of the underlying between-subject standard deviation (SD) to the within-subject SD was calculated from duplicates. Correlation coefficients between pairs were adjusted to include an estimate of the underlying correlation.

Results: Mean values [day 1 (1SD)] were 143 (36) mg/dl (non-HDL-C) and 98 (24) mg/dl (apoB). The DR's of both parameters were similar (1.76 and 1.83) (p = 0.83). Pearson's product-moment correlation coefficient between tests was very high (0.94), reaching unity (1.00) after attenuation adjustment. The unbiased equation of equivalence relating apoB to non-HDL-C had a slope of 0.65 and an intercept of 6.3 mg/dl.

Conclusions: The discrimination power of non-HDL-C is similar to that of apoB to rank diabetic patients according to atherogenic cholesterol and lipoprotein burden. Since true correlation between variables reached unity, non-HDL-C may provide not only a metabolic surrogate but also a candidate biometrical equivalent to apoB, as non-HDL-C calculation is readily available.

Figure 1

Plots of untransformed values obtained on day 1 (X axis) and day 2 (Y axis) for non-HDL-cholesterol (non-HDL-C; left panel) and apolipoprotein B₁₀₀ (ApoB; right panel) ratios in n = 45 subjects with diabetes mellitus.

Figure 2

Plots of means of duplicate measurements obtained on day 1 and day 2 for non-HDL-cholesterol (non-HDL-C; X axis) and apolipoprotein B₁₀₀ (ApoB; Y axis) in n = 45 subjects with diabetes mellitus. The line represents the uncorrected linear regression equation relating non-HDL-C and apolipoprotein B₁₀₀ [ApoB = 0.60 (non-HDL-C) + 12]. The insert box provides the unbiased equivalence equation which calculates ApoB from non-HDL-C based on the discriminant ratio methodology. R² represents the measured Pearson correlation coefficient between tests, prior to attenuation adjustment.