The reproducibility of the modified relative dose response (MRDR) assay in healthy individuals over time and its comparison with conjunctival impression cytology (CIC).

The modified relative dose response (MRDR) assay is a minimally invasive method of detecting marginal vitamin A status. In the present study, the MRDR assay was performed four times in six well-nourished adults and in one male five-year-old child over a seven-month period. In all instances, assay ratios of dehydroretinol (DR) to retinol (R) were less than 0.03, the tentative cutoff value of 'normal' for the MRDR assay in humans. The mean ratio for all time points for all individuals was 0.015 +/- 0.005, with a mean coefficient of variation of 27 +/- 13%. In a related experiment, both MRDR and conjunctival impression cytology (CIC) tests were conducted on nine adults and the same male child. All DR/R ratios were less than or equal to 0.021, and all CIC specimens were normal. Thus, the DR/R ratio in well-nourished individuals, although showing some variation, does not oscillate between abnormal and normal responses. Furthermore, the DR/R ratios and CIC patterns were fully concordant.