Protein-energy malnutrition and liver dysfunction limit the usefulness of the relative dose response (RDR) test for predicting vitamin A deficiency.

The relative dose response (RDR) test was examined for its value in predicting vitamin A nutriture among chronically ill patients with protein-energy malnutrition and among patients with varying degrees of liver dysfunction. The RDR test was elevated (ie greater than 14 per cent) and, thus, predictive of vitamin A deficiency in only 4 out of 9 patients with combined vitamin A deficiency and protein-energy malnutrition. Among 27 patients with liver dysfunction who had vitamin A determinations performed on liver biopsy material, there was no correlation found between the RDR response and the hepatic vitamin A level. Of 12 patients with low hepatic vitamin A levels (less than 100 micrograms/g wet weight), the RDR test was normal in 9 (75 per cent). Inability of the RDR test to predict vitamin A nutriture in patients with protein-energy malnutrition and in patients with liver dysfunction may, in part, be due to inadequate synthesis or release of retinol-binding protein.