FIGURE 4.

The relation of the modified relative dose-response (MRDR) value to liver retinol concentrations in piglets. Below 17 μg retinol/g liver, the MRDR value was invariably positive (ie, ≥0.060); between 17 and 29 μg retinol/g liver, the response was split; and at >29 μg retinol/g liver, the MRDR value was usually <0.060. The solid lines are the current accepted cutoffs to define vitamin A deficiency. The dashed lines define the areas where the MRDR value had the best sensitivity to reflect deficient and adequate vitamin A status defined by liver reserves.