Vitamin B12 (cobalamin) plays an important role in DNA synthesis and neurologic function. Deficiency can lead to a wide spectrum of hematologic and neuropsychiatric disorders that can often be reserved by early diagnosis and prompt treatment.1 Laboratory testing is used to detect a vitamin deficiency, determine its severity, establish it as the underlying cause of someone's symptoms, and monitor the effectiveness of treatment.5
The primary analysis of vitamin B12 deficiency is the measurement of serum cobalamin (vitamin B12).2 The commonly used tests measure total vitamin B12, which is found in blood bound to two carrier proteins:
- Haptocorrin (HC)
- Transcobalamin (TC)
When vitamin B12 is bound to transcobalamin it is referred to as holotranscobalamin (holoTC). HoloTC is also known as active-b12, as it contains the biologically available cobalamin and only holoTC promotes the uptake of cobalamin by all cells via specific receptors.
In comparison, approximately 80% of the circulating cobalamin that is carried by haptocorrin is considered metabolically inert because no cellular receptors exist (with the exception of receptors found in the liver).3