The modified relative-dose-response assay as an indicator of vitamin A status in a population of well-nourished American children.

The relative-dose-response (RDR) assay first proposed by Underwood has proved to be a useful indicator of marginal vitamin A status. We suggested that 3,4-didehydroretinol might be used in a simpler assay that requires only one blood sample for analysis. In the present study 24 healthy children aged 3.7-7.1 y were given 100 micrograms 3,4-didehydroretinyl acetate/kg body wt in corn oil, followed by ice cream (90 mL). A blood sample was taken 2, 4, 5, 6, 8, 10, or 24 h after the dose. The mean ratio of dehydroretinol to retinaol (DR-R ratio) plateaued at approximately 0.02 in the plasma between 4 and 10 h. Only three children showed ratios greater than 0.03. Upon reinvestigation, the DR-R ratio remained greater than 0.03 in one child at 5 h. After vitamin A treatment the ratio decreased to 0.019. Thus, a tentative DR-R cutoff ratio for a satisfactory vitamin A status in healthy American children is 0.03.