Use of free and transthyretin-bound retinol-binding protein in serum as tests of vitamin A status in humans: effect of high creatinine concentrations in serum.

We measured immunologically active (apo + holo) retinol-binding protein (RBP), vitamin A-carrying (holo) free RBP, and transthyretin-bound (TTR) holo-RBP in serum from 34 retrospective cases of fluctuating acute renal failure. All subjects had high serum creatinine concentrations caused by renal failure. Apo + holo, holo-TTR-RBP, and (especially) holo-free RBP all correlated poorly but significantly with serum creatinine concentration. Therefore, the use of any form of RBP to measure vitamin A status may be of limited value in subjects with high creatinine concentrations in serum. However, molecular-exclusion HPLC may be able to distinguish increases in RBP concentration associated with renal failure from those caused by altered vitamin A status, because renal failure causes abnormalities in the number and retention times of chromatographic peaks as well as their areas.