COMPARISON OF THE MODIFIED RELATIVE DOSE-RESPONSE (MRDR) AND THE RELATIVE DOSE-RESPONSE (RDR) IN THE ASSESSMENT OF VITAMIN-A STATUS IN MALNOURISHED CHILDREN

The modified-relative-dose-response (MRDR) test and the relative-dose- response (RDR) test were compared in 49 mildly to moderately malnouris hed Bangladeshi children. The MRDR test had a significantly lower sens itivity, detecting only 71% of children with very low serum retinol (l ess than or equal to 0.35 mu mol/L) and 33% of children with low serum retinol (0.355-0.70 mu mol/L) compared with 100% and 80% for the RDR test, respectively. The MRDR test showed a very strong dependency on r etinol-binding protein (REP) saturation (ie, percent saturation of REP with retinol) compared with the RDR test. Only 3 (23%) of 13 children with REP saturation greater than or equal to 55% but low vitamin A st ores were diagnosed as abnormal by the MRDR test. This suggests that w hen apo-RBP concentration is limiting, as it is in malnourished childr en, didehydroretinol, the analog used in the MRDR test cannot effectiv ely compete with retinol for binding to apo-RBP. Under these circumsta nces, the MRDR test is rendered ineffective. The possibility of increa sing the sensitivity of the test by using a high dose of didehydroreti nol needs to be investigated.