Variability of lipid measurements: relevance for the clinician.

Decreasing the large test variability associated with measurements of blood cholesterol, triglyceride, and high-density lipoprotein (HDL)- and low-density lipoprotein (LDL)-cholesterol is likely to improve the classification of coronary heart disease (CHD) risk and allow improved monitoring of lipid-lowering treatments. However, improving test precision will benefit the clinician only if (a) the analytical test variability is high relative to the biological test variability and (b) detecting subtle responses to diet or drug therapy is clinically important. Improving HDL- and LDL-cholesterol test precision can be expected to increase the clinical usefulness of these measurements because values for HDL- and LDL-cholesterol correlate closely with CHD risk; are associated with small, yet clinically important, changes in response to diet and (or) drug therapy; and have substantial analytical test variability relative to biological variability. On the other hand, measurements of both blood cholesterol and triglyceride have high biological relative to analytical variability, and do not correlate as closely with CHD risk. Therefore, further improvements in precision for these measurements are less likely to be useful to the clinician.