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Journal of the American College of Nutrition, Vol 15, Issue 5 450-457, Copyright © 1996 by American College of Nutrition

JOURNAL ARTICLE

Reproducibility of relative dose response (RDR) test and serum retinol and retinyl ester concentrations in children after a 2-week interval

J. Apgar, D. Makdani, A. L. Sowell, E. W. Gunter, A. Hegar, D. Rao and J. C. Smith
US Plant, Soil, and Nutrition Laboratory, Ithaca, New York, USA.

OBJECTIVE: Reproducibility of the relative dose response test (RDR), a test designed to measure vitamin A status, was tested in 23 Belizean children, 5-8 years after 2-week interval during which no treatment was given. METHODS: As required for the RDR test, serum retinol concentrations were determined before and 5 hours after an oral dose of vitamin A. An RDR score > 14% was used as the criterion of inadequate vitamin A status. The HPLC method used to measure serum retinol concentrations also determined the concentrations of four retinyl esters. RESULTS: The RDR test was reproducible for 17 of 23 subjects: 3 scored > 14% on both tests; 14, < 14% on both. Six subjects scored > 14% on only one test. The concordance correlation coefficient (rc) for the percent change in the two tests was 0.24; for fasting serum retinol concentration, rc = 0.81. For retinyl palmitate and stearate, the esters present in highest concentrations at 5 hours, concordance correlation coefficients were 0.75 and 0.59, respectively. CONCLUSION: The failure of the RDR test to classify 26% of the subjects reproducibly reduces the usefulness of the test. In addition, the reproducibility of the retinyl ester concentrations in serum 5 hours after the retinyl palmitate dose and the relatively high concentrations in some subjects suggests that some individuals may not metabolize sufficient retinol in 5 hours to cause a maximal increase in serum retinol, resulting in an underestimation of deficiency in a population in which the RDR test is used.


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