Intra-individual variation in serum vitamin A measures among participants in the Third National Health and Nutrition Examination Survey, 1988-1994
Gillespie, Cathleen Doris
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Background: The biologic variability in serum retinol and retinyl esters has never been assessed in a large population based study. Objective and Design: Using data from the Third National Health and Nutrition Examination Survey, 1988-1994, we estimated the biological coefficient of variation and examined associations with other factors. We estimated 95% prediction intervals for the NHANES III sample. We evaluated the predictive value of using a single concentration or measurement to classify participants’ vitamin A status. Results: Serum retinol measures appear to be fairly stable among adults. The greatest variation occurs in minorities and children <12 years, groups known to be at a higher risk of hypovitaminosis A. There is evidence of high analytic and biologic variation in serum retinyl esters measures. Conclusions: Published population estimates may be unreliable, particularly for serum retinyl esters. Repeated serum measurements are required to accurately assess vitamin A status at the clinical level.