Factors affecting the concentration of free holo retinol-binding protein in human plasma.

The total concentrations of retinol, retinol-binding protein and prealbumin were determined in plasma from twenty healthy men and sixty patients with various inflammatory conditions. These concentrations were all strongly correlated to each other and lower in the patient group. The concentration of free (not prealbumin-bound) holo retinol-binding protein, the presumed 'active' supplier of retinol to the tissues, was calculated. It was found not to be decreased in the patient group. Of the measured total concentrations and their possible ratios in the whole material, the retinol/prealbumin ratio showed the strongest correlation to the concentration of free holo retinol-binding protein. The importance of the concentration of free holo retinol-binding protein for the vitamin A supply to the cells was supported by calculations on data from the literature showing that this concentration better than the above-mentioned total concentrations distinguished between patients with normal and abnormal dark adaptation ability.