Biological variability in concentrations of serum lipids: sources of variation among results from published studies...

To obtain the best estimates of the average intraindividual biological variability (CVb) in the concentrations of total cholesterol (TC), low-density lipoprotein cholesterol (LDLC), high-density lipoprotein cholesterol (HDLC), and triglyceride serum lipids in a person's blood, we evaluated results from 30 studies published from 1970 to 1992. The usually more applicable random-effects model estimated an average CVb of 6.1% for TC, 7.4% for HDLC, 9.5% for LDLC, and 22.6% for triglyceride. Composite estimates of the average CVb from all evaluated published studies by different models of estimation ranged from 6.0% to 6.4% for TC, from 6.2% to 7.5% for HDLC, from 7.0% to 9.6% for LDLC, and from 22.4% to 22.9% for triglyceride. Two important factors influenced the reported biological variation of the study subjects: (a) the magnitude of the variability of the analytical method used and (b) the design characteristics of the study--primarily the number of subjects, the sampling interval, and the number of measurements per subject. For TC, we found a statistically significant positive correlation between the reported mean CVb and both the number of study subjects and the analytical variation. For TC and LDLC we estimate CVb as a function of the study design features. The number of patient specimens required to obtain reliable estimates for serum lipid concentrations are determined from the CVb and the current analytical variation.