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The variation of serum cholesterol level was studied in a cohort of 16,281 individuals, with repeated measurements of cholesterol. The mean correlation coefficient between the two cholesterol values taken with a six-week interval on two occasions was 0.74. This correlation coefficient indicates a short-term variation of serum cholesterol, and reflects measurement errors and intra-individual fluctuations in cholesterol level, eg due to variations in dietary habits. The correlation coefficient for serum cholesterol values taken with a two-year interval was 0.66 and reflects a long-term variation. The ratio between these coefficients may be interpreted as a rough estimate of a correlation between the true cholesterol levels at a two-year interval, free from measurement errors and short-term intra-individual variations in dietary habits. The validity was assessed with the correlation between a single serum cholesterol value and mortality from myocardial infarction, in a cohort of 92,839 individuals followed-up for 14-16 years. The relative risks (RR) for death in myocardial infarction increased with increasing cholesterol levels. The RRs were in accordance with the well-established correlation between serum cholesterol and death from myocardial infarction. The results indicated a fairly high stability of the cholesterol level in blood and that the cholesterol values in the studied cohort were not less reliable than in comparable studies.
Törnberg et al. (Fri,) studied this question.