Response to Letter Regarding Article, “Fasting Compared With Nonfasting Lipids and Apolipoproteins for Predicting Incident Cardiovascular Events”
We thank Drs Lund, Vaag, and Jensen for their interest in and thoughtful comments on our study.1 In response to their question about the measurement of low-density lipoprotein (LDL) cholesterol concentration by a direct assay on frozen samples, we have previously examined time-to-processing conditions for the direct homogeneous LDL cholesterol assay that we used (Roche Diagnostics, Indianapolis, Ind) and found no significant changes in direct LDL cholesterol concentrations measured on frozen samples up to 6 months, with excellent reproducibility compared with fresh samples. Data on the predictive performance of direct LDL cholesterol assays in relation to clinical events and how they compare with the Friedewald calculation are sparse.2 When the Friedewald equation was used to calculate LDL cholesterol concentration in this study, the associations of fasting and nonfasting Friedewald LDL cholesterol with cardiovascular disease events were very similar to the results obtained using the direct LDL cholesterol assay. In summary, our study findings suggest that nonfasting blood draws may suffice for initial screening of cardiovascular risk with the use of the total/high-density lipoprotein cholesterol ratio, high-density lipoprotein cholesterol, and triglycerides, consistent with recent data published from the Copenhagen City Heart Study on the clinical utility of nonfasting lipid measurements in a general Danish population of men and women.3
Mora S, Rifai N, Buring JE, Ridker PM. Fasting compared with nonfasting lipids and apolipoproteins for predicting incident cardiovascular events. Circulation. 2008; 118: 993–1001.
Friedewald WT, Levy RI, Fredrickson DS. Estimation of the concentration of low-density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifuge. Clin Chem. 1972; 18: 499–502.
Langsted A, Freiberg JJ, Nordestgaard BG. Fasting and nonfasting lipid levels: influence of normal food intake on lipids, lipoproteins, apolipoproteins, and cardiovascular risk prediction. Circulation. 2008; 118: 2047–2056.