Standardization of total cholesterol measurement in population surveys--pre-analytic sources of variation and their effect on the prevalence of hypercholesterolaemia.

BACKGROUND: The estimation of population distribution of total cholesterol, as well as other blood lipids requires population surveys. Comparability of the estimates over time or between populations requires a predefined, standardized measurement protocol. This paper will assess the effect of variation in the pre-analytic procedures, on the estimation of population distribution of total cholesterol and the prevalence of hypercholesterolaemia. Implications of variation to real survey results are demonstrated on data collected during the WHO MONICA Project. DESIGN AND METHODS: The extent (%) of pre-analytic variations were determined by literature review. Simulations were then used to estimate the effect of these variations on the distribution of total cholesterol values. Three populations were selected as examples for different population distributions of total cholesterol levels and variations resulting from seasonal and postural changes, use of tourniquet, and serum versus plasma collection were simulated both individually and in combinations.
RESULTS: Depending on the population distribution of total cholesterol, differences in pre-analytic procedures can explain a difference of up to 1.12 mmol/l in the mean total cholesterol between populations, and a difference up to 41% in the prevalence of hypercholesterolaemia (> or =6.5 mmol/l).
CONCLUSIONS: Variation in results on measured total cholesterol levels due to differences in procedures during the pre-analytic stage can diminish substantially the reliability and comparability of measurements among surveys over time and between populations. The effect of pre-analytic variation in the population estimates of total cholesterol can be extensively reduced by standardization and training.