TABLE 1.

Selected reference intervals for holotranscobalamin (holoTC) with the use of the most common assays for holoTC measurement¹

Method2	Sample	Reference range	n	Reference
	μL	pmol/L
Radioimmunoassay	400	24–160	105	22
		37–170	303	28
Microbiology	<150	42–160	500	9
ELISA	100	40–150	137	23
Direct	200	19–130	292	26
		36–220	276	50

¹ELISA, enzyme-linked immunosorbent assay.

²Radioimmunoassay: precipitation of transcobalamin on antibody-coated beads and measurement of vitamin B-12 with the use of an isotope dilution method. Microbiology: precipitation of transcobalamin by antibody-coated beads and measurement of trapped vitamin B-12 with the use of a microbiological method. ELISA: measurement of holoTC with the use of ELISA after removal of apotranscobalamin with vitamin B-12–coated beads. Direct: measurement of holoTC by ELISA, with the use of an antibody that is specific for holoTC.