Estimates of the average intra-individual biological variability for plasma
lipids and lipoproteins differs substantially among published studies. Mor
eover, this topic does not appear to have received consideration in exercis
e and health literature with normal, healthy children as subjects. The purp
ose of this study was, therefore, to determine the short-term day-to-day va
riability of the lipid-lipoprotein profile from 19 children [mean (SD), 11.
5 (0.8) years] from 3 separate venous blood samples. Intra-individual stand
ard deviations, variances and coefficients of variance were determined for
total cholesterol (TC), triacylglycerol (TG), high-density lipoprotein-chol
esterol (HDL-C), HDL-C sub-fractions HDL2 and HDL3, and low-density lipopro
tein-cholesterol (LDL-C). The intra-individual variation for TC and LDL-C w
as used to calculate the 95% confidence intervals (CIs) around the National
Cholesterol Education Programme (NCEP 1991) cut-off points. The main findi
ng was that all of the measured blood analytes including TC, TG, HDL-C, HDL
2, HDL3, and LDL-C varied considerably from day-today. Coefficients of tota
l variation ranged from 3.5% for HDL3 to 25.4% for TG. Classification of in
dividuals using NCEP guidelines was difficult based on only one or two bloo
d samples. The magnitude of variation for LDL-C meant that a 95% CI could n
ot be constructed around the NCEP borderline-high classification from eithe
r one or two samples. However, averaging three TC and LDL-C measurements in
creased the likelihood of classification within the 95% CI. The results ind
icate that when using the NCEP guidelines for children and adolescents, tru
e concentrations for TC and LDL-C should be based on the mean of multiple s
amples.