TABLE 1.

Typical reference ranges and cutoff values for blood biomarkers of vitamin B-12 status in adults¹

Blood biomarker	Typical reference ranges	Typical cutoff values
Serum total vitamin B-12	148–664 pmol/L (200–900 pg/mL)	Deficiency: <148 pmol/L (<200 pg/mL)
		Insufficiency: 148–221 pmol/L (200–300 pg/mL)
Serum holoTC	40–150 pmol/L	Deficiency: <35–40 pmol/L
Serum MMA	50–370 nmol/L	Elevated: >370 nmol/L
Plasma total Hcy	4–10 µmol/L	Elevated: >12–15 µmol/L
cB12	Not available	Adequacy: –0.5 to 1.5
		Low: –1.5 to –0.5
		Possible deficiency: –2.5 to –1.5
		Probable deficiency: <–2.5
		Elevated: >1.5

¹cB12, combined vitamin B-12; Hcy, homocysteine; holoTC, holotranscobalamin; MMA, methylmalonic acid.