Human serum retinol transport in malabsorption

Using specific immunoassays for retinol-binding protein (RBP) and prealbumin (PA), the proteins responsible for serum vitamin A transport in man, the retinol transport system has been examined in 22 adults with malabsorption (mean stool fat 23 g/24 hr). Mean serum concentrations of vitamin A and RBP in these patients did not differ from normal, whereas PA levels were depressed (P < 0.001). This contrasted with the previously reported marked depression of all three components of the serum retinol transport system in patients with liver disease and the marked elevations of vitamin A and RBP in patients with renal failure. In patients with malabsorption, serum concentrations of vitamin A were correlated with RBP (r = 0.901, P < 0.001). These data are consistent with the hypothesis that patients effectively mobilize hepatic stores of vitamin A as a retinol-RBP complex during fat malabsorption. For this reason, serum vitamin A concentrations are a poor means of screening for malabsorption.