Evidence-Based Nutrient Recommendations

Vitamin B12 Metabolism-Related Lab Values

Serum B12 is measured in both pmol/l and pg/ml with a conversion factor of 1.35 pg/ml = 1 pmol/l (1).

Average Daily B12 Intake of USA Adults2
Men 5 µg
Women 3.5 µg
Normal Serum B12
Range, newborns3 160 – 1300 pg/ml
Range, adultsA 200 – 900 pg/ml
Average 450 pg/ml
Breast MilkB,4 180 – 300 pg/ml
Normal MCV Range5 80-96 fl
Methylmalonic Acid (MMA)
Normal serum MMA (sMMA) .07 – .27 µmol/l(6, 7)
Serum MMA cutoff in diagnosing B12 deficiency .376 µmol/l7
Normal urine MMA (uMMA) .58 – 3.56 µmol/mmol Cr8
Homocysteine (HCY)
Normal serum HCY 2.2 – 13.2 µmol/l9
A – sB12 does not change more than 7% from week to week under normal
conditions (i.e. consistent intake, no disease)11.
B – Numbers vary widely depending on measurement methods and
differences in maternal stores and intake.


1. Tucker KL, Rich S, Rosenberg I, Jacques P, Dallal G, Wilson PW, Selhub J. Plasma vitamin B-12 concentrations relate to intake source in the Framingham Offspring study. Am J Clin Nutr. 2000 Feb;71(2):514-22.

2. Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington, DC: National Academy Press; 2000.

3. Fischbach F. A Manual of Laboratory & Diagnostic Tests, 6th Ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2000.

4. Kuhne T, Bubl R, Baumgartner R. Maternal vegan diet causing a serious infantile Neurological disorder due to vitamin B12 deficiency. Eur J Pediatr. 1991 Jan;150(3):205-8.

5. Stedman’s Medical Dictionary, 26th ed. Baltimore: Williams & Wilkins, 1995.

6. Kuzminski AM, Del Giacco EJ, Allen RH, Stabler SP, Lindenbaum J. Effective treatment of cobalamin deficiency with oral cobalamin. Blood. 1998 Aug 15;92(4):1191-8.

7. Holleland G, Schneede J, Ueland PM, Lund PK, Refsum H, Sandberg S. Cobalamin deficiency in general practice. Assessment of the diagnostic utility and cost-benefit analysis of methylmalonic acid determination in relation to current diagnostic strategies. Clin Chem. 1999 Feb;45(2):189-98.

8. Rasmussen K, Moelby L, Jensen MK. Studies on methylmalonic acid in humans. II. Relationship between concentrations in serum and urinary excretion, and the correlation between serum cobalamin and accumulation of methylmalonic acid. Clin Chem. 1989 Dec;35(12):2277-80.

9. Loehrer FM, Schwab R, Angst CP, Haefeli WE, Fowler B. Influence of oral S-adenosylmethionine on plasma 5-methyltetrahydrofolate, S-adenosylhomocysteine, homocysteine and methionine in healthy humans. J Pharmacol Exp Ther. 1997 Aug;282(2):845-50.

11. Halsted JA, Carroll J, Rubert S. Serum and tissue concentration of vitamin B12 in certain pathologic states. N Engl J Med. 1959;260:575-80.

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