Clinical Nutrition

Lesson 6: Vitamin A Deficiency

The relative dose response (RDR) assay

A small dose of 1.6 – 3.5 µmol of retinyl ester in oil is given as an oral dose. In response to this, the liver releases apo-RBP (Retinol binding protein). The serum retinol concentrations before and five hours after the oral dose are measured. The ratio of the difference in serum retinol concentrations between the two time points is calculated and expressed as percentage and is the RDR.

If RDR is more than 20% it indicates inadequate hepatic stores or marginal vitamin A stores