COMPARISON OF METHODS OF ASSESSING VITAMIN-A STATUS IN CHILDREN

Objective: A study of children (2-8 years; n = 613) in Belize, Central America, was conducted to determine what proportion of the children m ight be at risk of vitamin A (vit A) deficiency. The data provide an o pportunity to compare results of three methods of assessing vit A stat us in a population which was not severely malnourished. Serum retinyl ester concentrations were also determined; their relevance to one of t he tests, the relative dose response (RDR) test is discussed. Methods: The three methods of assessing vit A status were: RDR test, fasting s erum retinol concentration, and conjunctival impression cytology (CIC) . Retinol-binding protein (REP), serum retinyl esters and serum zinc c oncentrations were also determined. Results: Inadequate vit A status w as indicated for 17% of subjects by the RDR test (14% cutoff), for 24% by fasting serum retinol concentration (<0.87 mu mol/L), and for 49% by ''abnormal'' CIC score. Retinyl esters constituted 24% of serum ret inoids at the time (5 hours after a retinyl palmitate dose) at which t he second blood sample is taken for the RDR test. Regression tree anal yses (CART) indicated ethnicity was a predictor of RDR score; ethnicit y, stunting and age were predictors of fasting serum retinol concentra tion; ethnicity and stunting were predictors of 0-hour retinyl ester c oncentration. Conclusion: The three indices of vit A status did not id entify the same individuals nor indicate the same percentage of the po pulation to be at risk for vit A deficiency. Increased concentrations of retinyl esters at 5 hours compared to those at 0 hours suggest that insufficient retinol may have been taken up by the liver at 5 hours t o release all accumulated retinol-binding protein (REP) in deficient i ndividuals; prevalence of vit A deficiency might therefore be underest imated by the RDR test The selection of ethnicity as a predictor of RD R score and of 0-hour retinol and retinyl ester concentrations suggest s that factors other than vit A status affect vit A metabolism and may affect the RDR test.