Plasma holotranscobalamin compared with plasma cobalamins for assessment of vitamin B12 absorption; optimisation of a non-radioactive vitamin B12 absorption test (CobaSorb)

BackgroundA recently developed non-radioactive vitamin B12 absorption test (CobaSorb) was further explored to identify the best marker for reflection of vitamin B12 absorption and to determine the duration of the test.MethodsSeventy-eight healthy individuals (age 21–81 years) were given three oral doses of 9 μg vitamin B12 per day for 5 successive days. Non-fasting blood samples were collected on days 1 to 5 before administration of vitamin B12 and on day 8. Cobalamins and holotranscobalamin were measured.ResultsPerformance of the vitamin B12 absorption test was evaluated in individuals with holotranscobalamin or cobalamins below the 75% percentiles. We used a change greater than 2 × CVday-to-day in holotranscobalamin (22%) and cobalamins (12%) to indicate a change caused by absorption of vitamin B12. Among individuals with a baseline holotranscobalamin below the 75% percentile (< 75 pmol/L, n = 57), 98% had an increase in holotranscobalamin > 22% from day 1 to day 3. In contrast, only 72% of the individuals with baseline cobalamins below the 75% percentile (< 335 pmol/L, n = 57) had an increase in cobalamins > 12%.ConclusionsIn healthy individuals with baseline holotranscobalamin < 75 pmol/L, vitamin B12 absorption is well reflected by an increase in holotranscobalamin after 2 days administration of oral vitamin B12.