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


CONCLUSIONS
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.
US Plant, Soil, and Nutrition Laboratory, Ithaca, New York, USA.
J
J
Apgar
D
D
Makdani
A L
AL
Sowell
E W
EW
Gunter
A
A
Hegar
D
D
Rao
J C
JC
Smith
D016588:Anticarcinogenic Agents / Q000097:blood*; D002648:Child; D002675:Child, Preschool; D002851:Chromatography, High Pressure Liquid; D004224:Diterpenes; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D008297:Male; D015203:Reproducibility of Results; D000084562:Retinyl Esters; D014801:Vitamin A / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000097:blood*
D016588:Anticarcinogenic Agents; D004224:Diterpenes; D000084562:Retinyl Esters; D014801:Vitamin A; C014794:retinol palmitate; C042811:retinyl stearate