Table 2.

Assessment of vitamin B₁₂ in human blood plasma.

Analyte	Reference Interval	B12 Deficiency	Advantages and Disadvantages
Total B12, pM	200–600	<148	Requires digestion of proteins
Holotranscobalamin, pM	40–100	<35	Highly automated
Homocysteine, μM	8–15	>15	Several confounders: B9 and B6 levels, thyroid function, glomerular filtration rate, sex, and age
2-methylmalonic acid, nM	0.04–0.37	>0.37	Results may be unreliable in cases of kidney deficiency or infection