Blood lipid measurements. Variations and practical utility

To describe the magnitude and impact of the major biological and analytical sources of variation in serum lipid and lipoprotein levels on risk of coronary heart disease; to present a way to qualitatively estimate the total intraindividual variation; and to demonstrate how to determine the number of specimens required to estimate, with 95% confidence, the "true" underlying total cholesterol value in the serum of a patient.

Representative references on each source of variation were selected from more than 300 reviewed publications, most published within the past 5 years, to document current findings and concepts. Most articles reviewed were in English.

Studies on biological sources of variation were selected using the following criteria: representative of published findings, clear statement of either significant or insignificant results, and acquisition of clinical and laboratory data under standardized conditions. Representative results for special populations such as women and children are reported when results differ from those of adult men.

References were selected based on acceptable experimental design and use of standardized laboratory lipid measurements.

The lipid levels considered representative for a selected source of variation arose from quantitative measurements by a suitably standardized laboratory. Statistical analysis of data was examined to assure reliability. The proposed method of estimating the biological coefficient of variation must be considered to give qualitative results, because only two or three serial specimens are collected in most cases for the estimation.

Concern has arisen about the magnitude, impact, and interpretation of preanalytical as well as analytical sources of variation on reported results of lipid measurements of an individual. Preanalytical sources of variation from behavioral, clinical, and sampling sources constitute about 60% of the total variation in a reported lipid measurement of an individual. A technique is presented to allow physicians to qualitatively estimate the intraindividual biological variation of a patient from the results of two or more specimens reported from a standardized laboratory and to determine whether additional specimens are needed to meet the National Cholesterol Education Program recommendation that the intraindividual serum total cholesterol coefficient of variation not exceed 5.0. A National Reference Method Network has been established to help solve analytical problems.