[Variation in serum cholesterol level in the same person: what is the true value and when is it called a significant...

The blood cholesterol level is not constant over time. Changing values may be found when rechecking high values, especially in patients on a diet or receiving medication. Repeated measurements are necessary. It will then be possible to estimate the 'true mean value'. This is the theoretical average of a large number of measurements taken from one person. The study concentrated on the intra-individual variation of the serum cholesterol and the consequences for screening and follow-up. For this purpose, during a period of four weeks, cholesterol levels were measured 12 times in 33 men aged 25-40. The mean coefficient of variation was 5.7%, with wide differences between participants, ranging from 2.9% to 9.8%. The position of the 'true mean value' was estimated (with 90% confidence), after I resp. 3 determinations. These findings have consequences for the classification of subjects in the different risk categories as defined in the Dutch Cholesterol Consensus. It is also possible to determine if, after a period of intervention, there is a significant decline in the cholesterol level. Roughly, a decline of 10-12% indicates a significant difference.