Cobalamin (Vitamin B12)

Total Cobalamin in Serum

Clinical Information

Also known as cobalamin, Vitamin B12 is critical for fat and carbohydrate metabolism and protein synthesis. It also has a role in folic acid metabolism1.

It is necessary for red blood cell production, DNA synthesis, and is a co-factor for enzymes involved in the conversion of homocysteine to methionine2.

Signs and Symptoms of Deficiency or Toxicity

Signs and symptoms of deficiency include macrocytic anemia, glossitis, peripheral neuropathy, wekness, ataxia, poor coordination among others3.

Vitamin B12 deficiency is often due to the lack of intrinsic factor (IF) in the gastric mucosa or malabsorption3.

The features of Vitamin B12 deficiency are megaloblastic anemia, fatigue, weakness, constipation, anorexia, and weight loss. Numbness and tingling sensations in the hands and feet are also observed. Other symptoms are depression, confusion, dementia, poor memory, and soreness of the mouth and tongue2.

Biomarker and Methods of Analysis


Vitamin B12 intake from food and supplements is converted to active cobalamins inside the body. Based on WHO International Guidelines. Vitamin B12 can be analyzed in serum using microbiological assays which quantifies total cobalamin. Serum concentration measures the amount of cobalamin available for use3,4,5.

Supplementation Guide

There is no supplementation guide for the general public. Treatment of clinical vitamin B12 deficiency is often thru intramuscular injections.

There is no established clinical guideline for the treatment of subclinical vitamin B12 deficiency6.

There is no established UL because there is no toxicological basis for a recommendation. However, 3 mg is suggested for observed safe level7.

Vitamin B12 may potentially interact with Chloramphenicol, proton pump inhibitors, H2 receptor antagonists, and metformin2.

Food Sources

Fish and red meats are rich sources. Poultry and eggs also contain vitamin B122.

(1) Huskisson E, Maggini S, Ruf M. The role of vitamins and mineral in energy metabolism and well-being. The Journal of International Medical Research 2007; 35: 277-289
(2) Office of Dietary Supplements-National Institutes of Health. Vitamin B12. Fact Sheet for Health Professionals. Retrieved from
(3) Mayo Clinic Medical Laboratories. (n.d.). Test Catalog. Vitamin B12 and Folate, Serum. Retrived from
(4) A Proposed INternational Standard for Vitamin B12 and serum folate. Report of the International Collaborative Study to Evaluate a Batch of Lymphilised Serum for B12 and Folate Content.
(5) Bralley, J.A., Lord, R.S. (2012). Laboratory Evaluations for Integrative and Functional Medicine. 2nd ed. Duluth, Ga: Metametrix Institute.
(6) Langan RC, Zawistoski KJ. Update on Vitamin B12 Deficiency. Retrieved from
(7) Hathcock , John H. Safety of Vitamin and Minral Supplements. Safe Levels Identified by Risk Assessment. April 2004.