Active B12 (holoTC)

The current convention is to estimate the abundance of vitamin B12 using total serum vitamin B12 as the first-line screen for deficiency. However this test has a low sensitivity. Up to 45% of vitamin B12-deficient/insufficient subjects may be overlooked if only serum B12 is used as a screening test. Active B12 (holotranscobalamin - holoTC) is the metabolically active portion of B12. Emerging evidence indicates that a low level of Active B12 is a more reliable marker of impaired vitamin B12 status than a low level of serum vitamin B12. Moreover unlike serum B12, Active B12 is believed to be stable in pregnancy. Several studies support Active B12 measurement as a first-line diagnostic test, and suggest that Active B12 may be the earliest marker for B12 depletion.