Relative-dose-response test

RDR = (A₅-A₀)/A₅×100%

Normal value should be <20%

Normal plasma vitamin A concentration in infants is 300~500 μg/L, in older children and adults it is 300~800 μg/L; when <200 μg/L, vitamin A deficiency can be diagnosed, 200~300 μg/L is considered subclinical deficiency.

The RDR test can confirm: A₀ is the fasting plasma vitamin A concentration, take 450 μg of vitamin A with breakfast, recheck the plasma vitamin A concentration A₅ 5 hours later before lunch, and calculate the RDR value using the formula to indicate liver vitamin A reserves.

If the RDR value is >20%, it indicates that liver vitamin A reserves are <70 μmol/(20 mg)/kg, and subclinical vitamin A deficiency can be diagnosed.