Diurnal and monthly intra-individual variability of the concentration of lipids, lipoproteins and apoproteins

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Abstract
Diurnal and monthly variability of the serum concentration of lipids, lipoproteins and apoproteins were examined in 11 healthy subjects aged 32-63 (mean 46) years. For diurnal measurements, blood samples were drawn at 0800, 1200, 1500,1800, and 2100 hours. The variability over 1 month was assessed from four analyses taken weekly at 0800 hours after at least 8 h fast. The analytical variability expressed as mean coefficient of variation (CV) ranged from 0.95% for cholesterol to 7.6% for apoprotein B. The mean CVs for diurnal biological variability were 2.4% for cholesterol, 3.5% for HDL-cholesterol, 5.1% for LDL-cholesterol, 29.5% for triglycerides, 6.5% for apoprotein A and 6.5% for apoprotein B. The respective biological CVs for monthly variability were 4.2%, 4.1%, 5.2%, 20.7%, 9.4% and 9.7%. A repeated-measures ANOVA revealed a significant increase of triglycerides (p<0.01) and decrease of LDL-cholesterol (p<0.01) during the day. Within 1 month, apoprotein A tended to rise (0.05<p<0.10). Although the best reproducibility was found for cholesterol, the results obtained indicate that six tests have to be taken before and after intervention by drug or diet to detect a reduction of 10% in an individual with a probability of 0.95.
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