Calculated low density lipoprotein cholesterol levels frequently underestimate directly measured low density lipoprotein cholesterol determinations in patients with serum triglyceride levels ≤ 4.52 mmol/l:: An analysis comparing the LipiDirect® magnetic LDL assay with the Friedewald calculation

Background: Increased low density lipoprotein cholesterol (LDL-C) is an established risk factor for the development of coronary artery disease (CAD). Recent guidelines detail specific LDL-C cutpoints for therapeutic goals. In practice, LDL-C is usually derived from the Friedewald formula (FF). This calculation is known to be inaccurate with serum triglyceride (TG) concentrations > 4.52 mmol/l, however, its accuracy among relatively healthy patient cohorts with TG concentrations <= 4.52 mmol/l is less well studied. Methods: We studied 661 ambulatory adults with TG concentrations <= 4.52 mmol/l and no overt CAD. Fasting venous lipid panels were obtained. LDL-C was calculated from the FF and also directly measured with the LipiDirect (R) Magnetic LDL assay. Linear regression and paired t-test analyses were performed. Results: Calculated and directly measured LDL-C concentrations were significantly different (4.26 +/- 0.88 vs. 4.83 +/- 1.06 mmol/l respectively, p < 0.0001). In 93% of measurements directly measured LDL-C exceeded calculated LDL-C. Although calculated and directly measured LDL-C concentrations were related (R=0.90), the discrepancy between them increased linearly with increasing TG concentrations (R=0.67) and clinically important differences existed at normal or slightly increased TG concentrations. Concordant results for NCEP ATP-III risk categories. were present for only 48.1% of samples. Conclusions: Significant differences between calculated and directly measured LDL-C using the LipiDirect (R) Magnetic LDL assay exist in healthy subjects with TG <= 4.52 mmol/l. These differences are linearly related to TG concentrations and occur frequently at relatively low TG concentrations. (c) 2005 Elsevier B.V. All rights reserved.