Time-dependent variability in repeated measurements of cholesterol levels: clinical implications for risk misclassification and intervention monitoring.
Intraindividual variability (IIV) in total cholesterol levels based on measurements taken 1 week apart is compared with an estimate based on measurements taken 2 years apart. Single-subject 95% confidence intervals around the mean of two repeated measurements were Xi +/- 21 and +/- 28 mg/dl, respectively, and Xi +/- 30 and +/- 40 mg/dl for a single measurement. Comparing these results with published estimates over varying time intervals shows a trend of decreasing IIV with shorter intervals, suggesting that confidence interval widths based on short-term repeated measurements and those based on longer-term repeated measurements may differ more than previously assumed. The practical consequences are that: (1) the level of misclassification inherent in the National Cholesterol Education Program (NCEP) guidelines may be less than had been estimated; and (2) reliable cholesterol reductions resulting from dietary or other interventions may be somewhat easier to detect. These findings have implications for the cost-effectiveness of cholesterol screening strategies and interventions to reduce cholesterol.
Roeback
J R
JR
Department of Epidemiology, University of North Carolina, Chapel Hill 27599-7400.
Cook
J R
JR
Guess
H A
HA
Heyse
J F
JF
D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D015982:Bias; D016001:Confidence Intervals; D003362:Cost-Benefit Analysis; D017408:Guidelines as Topic / Q000592:standards; D006266:Health Education; D006801:Humans; D006937:Hypercholesterolemia / Q000097:blood* / Q000145:classification / Q000453:epidemiology / Q000517:prevention & control; D008297:Male; D008403:Mass Screening / Q000191:economics / Q000592:standards*; D008875:Middle Aged; D009010:Monte Carlo Method; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D012307:Risk Factors; D013997:Time Factors