Vitamin A deficiency is a cause of significant disease worldwide, especially among women and children. Simple, reliable techniques for evaluating vitamin A status in populations are necessary to assess the need for vitamin A supplementation initiatives and to monitor their effectiveness. The most commonly used indicator of vitamin A status is the serum retinol concentration. However, retinol is unstable when exposed to heat or light, and the techniques used to measure it in the blood require expensive and complicated laboratory equipment.
The serum concentration of retinol-binding protein (RBP), the carrier for retinol in the blood, appears to be a preferred alternative measure for serum retinol. RBP is a protein synthesized by the liver and released into the circulation in a 1-to-1 complex with retinol. Most importantly the techniques used to quantify serum RBP are easier and less expensive than those used for retinol, and RBP is considerably more stable with respect to light and temperature. This study showed good correlation between concentrations of RBP and those of retinol and reasonable sensitivity and specificity in predicting vitamin A deficiency.
American Journal of Clinical Nutrition February 2004;79(2) 218-225