Within- and between-subject variation in commonly measured anthropometric and biochemical variables

Background: The biological variation of some commonly assessed metabolic va riables in healthy subjects has not been studied extensively. The aim of th e study was to assess, in 12 healthy subjects (6 male and 6 female; mean (S D) age; 22.7 (1.5) years) following an overnight fast, the day-to-day varia tion of body fat (impedance method), triglycerides, nonesterified fatty aci d (NEFAs), glycerol, 3-hydroxybutyrate (3-OHB), lactate, glucose, insulin ( RIA), C-peptide, and glucagon on 12 consecutive days. Methods: Between- and within-subject coefficients of variation (CVG and CVW ) were estimated using a random effects analysis of variance, and assay var iation was subtracted to give the coefficient of within-subject biological variation (CVI). Individuality indices were calculated as CVW/CVG. Results: The overall means, CVI, and individuality indices were as follows: for body fat, 24.2%, 10%, and 0.3; for triglycerides, 0.61 mmol/L, 21%, an d 1.1; for NEFAs, 376 mu mol/L, 45%, and 1.4; for glycerol, 48 mu mol/L, 36 %, and 0.8; for 3-OHB, 43 mu mol/L, 61%, and 1.5; for lactate, 0.88 mmol/L, 31%, and 1.1; for glucose, 4.9 mmol/L, 4.8%, and 0.7; for insulin, 52 pmol /L, 26%, and 1.0; for C-peptide, 0.39 nmol/L, 24%, and 0.9; and for glucago n, 53 ng/L, 19%, and 0.8. Conclusions: The data presented here are necessary for the evaluation of se veral important metabolic variables in individual and group studies. The bi ological variation of some metabolites makes it difficult to characterize t he status of healthy subjects with a single measurement. (C) 1999 American Association for Clinical Chemistry.