Holo-transcobalamin is an indicator of vitamin B-12 absorption in healthy adults with adequate vitamin B-12 status

Background: It has been hypothesized that the response of holo-transcobalamin (holo-TC) to oral vitamin B -12 may be used to assess absorption. To develop a reliable clinical absorption test that uses holo-TC, it is necessary to determine the optimal timeline for vitamin B-12 administration and postdose assessment. Objective: The objective of this study was to assess the magnitude and patterns of change in the postabsorption response of holo-TC to oral vitamin B-12. Design: Adult (18 -49 y) male and female participants (n = 21) with normal vitamin B-12 status were given three 9-μg doses of vitamin B-12 at 6-h intervals beginning early morning (baseline) on day 1. Blood was drawn at 17 timed intervals over the course of 3 d for the analysis of holo-TC and other indicators of vitamin B-12 status. Results: Mean holo-TC increased significantly (P < 0.001) from baseline at 6 h (11%) and 24 h (50%). TC saturation increased significantly (P < 0.001) from baseline at 12.5 h (33%) and 24 h (50%). The mean cobalamin concentration changed significantly (P