The effect of recombinant human intrinsic factor on the uptake of vitamin B12 in patients with evident vitamin B12 deficiency.

We report on the use of recombinant human intrinsic factor (rhIF) in a new vitamin B12 absorption test. Holotranscobalamin (holoTC) was measured before and 24 hours after intake of three 9-mg doses of vitamin B12 (B12) and again 24 hours after intake of the same dose of B12 together with rhIF (rhIF-B12). Nine patients with evident vitamin B12 deficiency had a significantly higher increase in holoTC after intake of rhIF-B12 than after intake of B12. Twenty-eight patients with suspected vitamin B12 deficiency showed no additional increase in holoTC after intake of rhIF-B12. We conclude that rhIF promotes B12 absorption among patients with evident vitamin B12 deficiency.