The effect of VLDL particles on the accuracy of a direct LDL-cholesterol method in type 2 diabetic patients

Objective: To assess the accuracy of the direct method LDL-c Plus, in type 2 diabetic patients. Methods: LDL-c Plus was measured in 64 consecutive samples of type 2 diabetic patients and compared with betaquantification (BQ), Friedewald's and an alternative formula. LDL-c Plus was also measured in the VLDL (d<1.006 Kg/L) fraction of these samples and in total serum and the VLDL fraction of a phenotype III patient, before and after diluting it with saline or VLDL from normolipidemic subjects. Results: LDL-c Plus showed a significant, constant bias (-8.5 +/- 5.6%) against BQ which correlated with VLDL-cholesterol/total triglyceride ratio (r = 0.760, p < 0.0005); bias decreased to zero when the ratio increased. In the VLDL fraction of the diabetic patients and the phenotype III patient LDL-c Plus measured 20.7 +/- 11.6% and 56.2% of the cholesterol, respectively. Dilution with saline did not alter the latter percentage, whereas dilution with normolipidemic VLDL reduced it showing that LDL-c Plus recognized cholesterol-enriched particles in the d<1.006 Kg/L. Friedewald's formula also showed a significant, constant bias (-3.1 +/- 6.4%) against BQ, whereas the alternative formula did not (0.5 +/- 6.1%). Both calculations classified patients better than LDL-c Plus did at NCEP cut-off points. Conclusions: In type 2 diabetic patients, LDL-c Plus underestimates LDL-c but measures cholesterol associated to IDL particles in the d<1.006 Ka/L fraction. Although LDLc-Plus might be a better cardiovascular risk estimator when well standardized, at the moment, it does not seem to be superior to calculations. (C) 2003 The Canadian Society of Clinical Chemists. All rights reserved.