Vitamins & Minerals Fasting RequiredTurnaround: 6–12 hours (same day)

Vitamin B12 (Cyanocobalamin)

Also known as: Cobalamin Test, Serum B12, Active B12, Methylcobalamin Test

Parameters Measured in the Report

A breakdown of individual biomarkers and biological reference intervals typically found in your report:

Biomarker	Standard Range	Unit	What It Means
Serum Vitamin B12 (Total Cobalamin)	Normal: 200–900 Borderline: 200–300 Deficient: < 200	pg/mL (or 148–664 pmol/L)	Total circulating cobalamin bound to transcobalamin and haptocorrin transport proteins.

* Note: Reference ranges may vary slightly between testing instruments and reagent kits. Always refer to the reference interval printed on your specific pathology report.

Clinical Focus

Total concentration of water-soluble vitamin B12 (cobalamin) in blood serum.

Sample & Specimen

Venous blood (Serum tube)

Fasting Protocol

Overnight fasting of 6 to 8 hours preferred for optimal baseline serum cobalamin.

Turnaround Time

6–12 hours (same day)

What Is This Test?

Vitamin B12 (Cobalamin) is an essential water-soluble micronutrient required for two critical biochemical pathways: normal DNA synthesis during red blood cell maturation in bone marrow, and the maintenance of the myelin sheath that insulates and protects peripheral nerves. Humans cannot synthesize vitamin B12; it must be obtained from animal foods (dairy, eggs, meat, fish) or fortified foods. Because B12 absorption requires gastric intrinsic factor produced by stomach parietal cells and an intact terminal ileum, both dietary inadequacy and absorption defects can trigger deficiency.

Why Did Your Doctor Order This Test?

Physicians routinely prescribe the Vitamin B12 in the following clinical scenarios:

Neurological symptoms: tingling, "pins and needles" (paresthesias) in hands or feet, numbness, loss of balance

Cognitive symptoms: unexplained memory lapses, confusion, mood changes, brain fog, and depression

Macrocytic anemia flagged on CBC (elevated MCV > 100 fL)

Strict vegetarian or vegan diets without supplementation

Long-term use of acid-suppressing medications (PPIs like omeprazole, H2 blockers) or Metformin, which impair B12 absorption

How to Prepare Before Your Test

Fasting Requirement: Overnight fasting of 6 to 8 hours preferred for optimal baseline serum cobalamin.

Fasting for 6–8 hours prior is generally recommended.
Refrain from taking oral B12 supplements or multivitamin tablets for 48 hours before testing unless monitoring current therapy.

Understanding Your Results

What higher or lower readings generally mean in clinical practice:

If Values Are Higher Than Normal

Significantly elevated B12 (>1,000 pg/mL) without supplementation is unusual and can be associated with chronic liver disease (release of stored hepatic B12), myeloproliferative disorders, or advanced renal failure.

If Values Are Lower Than Normal

Values under 200 pg/mL indicate clinical deficiency, resulting in macrocytic megaloblastic anemia and progressive peripheral nerve demyelination. Prolonged untreated deficiency can cause permanent neurological impairment.

Frequently Asked Questions

Why are vegetarians and vegans particularly prone to B12 deficiency?

Vitamin B12 is produced by microorganisms and is naturally present almost exclusively in animal products (dairy, eggs, fish, meat). Plant foods do not naturally produce B12, so non-meat diets require fortified foods or supplements.

Related Laboratory Tests

Tests frequently prescribed together or used as follow-up investigations:

Folic Acid (Vitamin B9 / Serum Folate)

Circulating concentration of water-soluble Vitamin B9 (folate) essential for one-carbon metabolism and DNA synthesis.

Complete Blood Count (CBC / Hemogram)

Counts and evaluates red blood cells, white blood cells, hemoglobin, hematocrit, and platelets.

Iron Profile & Serum Ferritin

Serum Iron, Total Iron-Binding Capacity (TIBC), Transferrin Saturation (% Sat), and Stored Tissue Ferritin.

Medical & Diagnostic Disclaimer

This guide is published for educational and patient informational purposes only. It is not a substitute for professional medical evaluation, diagnosis, or clinical advice.

A laboratory result that falls slightly outside standard statistical reference intervals does not automatically indicate disease; conversely, a normal result does not guarantee the absence of medical conditions. Only your attending physician can interpret lab findings in the context of your medical history, physical exam, and symptoms.