Adjustments to the modified relative dose response (MRDR) test for assessment of vitamin A status minimize the blood volume used in piglets

The modified relative dose response (MRDR) test is widely used in public health research to assess vitamin A (VA) status of populations and individuals. However, method adjustments intended to make the test more useful in large field studies and/or less invasive have not been systematically verified. To compare the similarity between modified tests and the standard MRDR test, and validate both modified and standard tests against liver reserves of VA, we used a piglet model. Following the typical MRDR procedure, piglets (n = 10) were dosed with 5.3 mumol 3,4-didehydroretinyl acetate. Method adjustments were made to the postdose blood sample collection time to decrease both the amount of serum analyzed and sample throughput time. We collected 3 blood samples/piglet at 3, 5, and 7 h or 4, 6, and 8 h postdose. Postdose blood samples obtained between 4 and 7 h gave MRDR values that did not differ. Serum volumes as small as 200 muL, half the volume of the standard method, yielded accurate MRDR values. Method adjustments to reduce sample throughput time require further investigation. In conclusion, because 200 muL of serum can be used in the test, only 0.5 mL, as opposed to 1 mL of blood has to be collected from an individual. This adjustment allows for easier application of the test to individuals, especially infants, from whom it is difficult to obtain a large venous blood sample, thus increasing the utility of the test for researchers.