Unit Converter
Vitamin B12 (Cobalamin, Cyanocobalamin)
(Essential Water-Soluble Vitamin - Required for DNA Synthesis, Neurological Function & Red Blood Cell Formation)
Synonyms
- Vitamin B12
- Cobalamin
- Cyanocobalamin
- Hydroxocobalamin
- Methylcobalamin
- Adenosylcobalamin
- Anti-pernicious anemia factor
Units of Measurement
- pmol/L
- pg/mL
- pg/dL
- pg/100 mL
- pg%
- pg/L
- ng/L
Unit Conversions
Molecular Weight of Vitamin B12 ≈ 1355 g/mol (varies by form)
pmol/L ↔ pg/mL
1 pmol/L=1.355 pg/mL1\ \text{pmol/L} = 1.355\ \text{pg/mL}1 pmol/L=1.355 pg/mL 1 pg/mL=0.738 pmol/L1\ \text{pg/mL} = 0.738\ \text{pmol/L}1 pg/mL=0.738 pmol/L
pg/dL → pg/mL
1 pg/dL=0.01 pg/mL1\ \text{pg/dL} = 0.01\ \text{pg/mL}1 pg/dL=0.01 pg/mL
pg/mL ↔ pg/L / ng/L
1 pg/mL=1000 pg/L=1 ng/L1\ \text{pg/mL} = 1000\ \text{pg/L} = 1\ \text{ng/L}1 pg/mL=1000 pg/L=1 ng/L
pg/100 mL = pg% = pg/dL
Description
Vitamin B12 is a water-soluble cobalt-containing vitamin essential for:
- DNA synthesis (via methionine synthase)
- Myelin formation (neurological function)
- Erythropoiesis (RBC production)
- Fatty acid & amino-acid metabolism
Humans acquire B12 only from animal-derived foods.
Absorption requires:
- Intrinsic Factor (IF) from gastric parietal cells
- Terminal ileum for uptake
- Normal pancreatic enzymes
- Transcobalamin II for transport
B12 stores last 2–5 years, so deficiency develops slowly-except in malabsorption.
Physiological Role
1. DNA Synthesis
Cobalamin is required to convert homocysteine → methionine.
Deficiency → impaired thymidine synthesis → megaloblastic anemia.
2. Neurological Function
B12 is essential for:
- Myelin synthesis
- Neurotransmitter balance
- Spinal cord integrity
Deficiency may cause irreversible neuropathy.
3. Hematologic Function
Deficiency → ineffective erythropoiesis → macrocytosis.
4. Metabolism
Coenzyme for:
- Methylmalonyl-CoA mutase
- Methionine synthase
Clinical Significance
LOW VITAMIN B12
Most important clinical aspect.
Hematologic
- Macrocytic anemia
- High MCV
- Pancytopenia (late)
- Hypersegmented neutrophils
Neurological
- Peripheral neuropathy
- Ataxia
- Paresthesias
- Loss of vibration/position sense
- Subacute combined degeneration of spinal cord
- Cognitive decline / dementia
Neurological deficits can be irreversible.
GI Symptoms
- Glossitis (“beefy red tongue”)
- Anorexia
- Weight loss
Causes of Deficiency
1. Pernicious Anemia
Most common in adults.
Autoantibodies destroy parietal cells → ↓ Intrinsic Factor.
2. Malabsorption
- Ileal resection / Crohn’s disease
- Celiac disease
- Pancreatic insufficiency
- Bacterial overgrowth (SIBO)
- Tapeworm (Diphyllobothrium latum)
3. Dietary Deficiency
- Strict vegans
- Elderly
- Malnutrition
4. Drug-Induced
- Metformin
- PPIs / H2 blockers
- Nitrous oxide (N₂O anesthesia) → inactivation of B12
5. Increased Requirement
- Pregnancy
- Hyperthyroidism
Biochemical Markers
- ↑ Methylmalonic acid (MMA)
- ↑ Homocysteine
HIGH VITAMIN B12
Less common.
Causes:
- Liver disease (leakage)
- Myeloproliferative disorders
- Leukemia
- Renal failure
- High-dose supplementation
- Transcobalamin II deficiency (paradoxical high level)
High B12 is not harmful by itself-usually indicates underlying disease.
Reference Intervals
(Tietz 8E + Mayo + ARUP + BSH hematology guidelines)
Serum Vitamin B12
- 200 – 900 pg/mL
(= 148 – 665 pmol/L)
Borderline
- 150 – 300 pg/mL
→ check MMA and homocysteine
Deficiency
- <150 pg/mL (<110 pmol/L)
Neurological symptoms can occur even at “low-normal” levels
Diagnostic Uses
1. Evaluation of Macrocytic Anemia
Tied with folate testing.
2. Neurological Disorders
Rule out reversible causes of neuropathy/dementia.
3. Pernicious Anemia Diagnosis
Combine B12 with:
- Anti-intrinsic factor antibodies
- Anti-parietal cell antibodies
4. Monitoring After Bariatric Surgery
Risk of severe malabsorption.
5. Elderly Population Screening
Common subclinical deficiency.
6. Pregnancy & Lactation
Increased demand.
7. Assessing Malabsorption Syndromes
Crohn’s, celiac, pancreatic disease.
Analytical Notes
- Serum B12 fluctuates; borderline values need MMA.
- Hemolysis has minimal effect; bilirubin may interfere depending on platform.
- LC-MS/MS or immunoassays are standard.
- Methylmalonic acid is more sensitive for early deficiency.
Clinical Pearls
- Neuropathy may occur without anemia.
- B12 deficiency + high folate intake → worsened neurological damage.
- Always treat suspected deficiency immediately-do not wait for confirmatory testing in symptomatic patients.
- Metformin causes B12 depletion → annual monitoring recommended.
- In elderly, low B12 is associated with falls, depression, and cognitive decline.
Interesting Fact
Vitamin B12 is the largest and most structurally complex vitamin known, containing a rare cobalt atom at its core.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Vitamins
- British Society for Haematology (BSH) - B12/Folate Guidelines
- NIH Office of Dietary Supplements - Cobalamin
- Mayo Clinic Laboratories - Vitamin B12
- ARUP Consult - Vitamin & Anemia Evaluation
- WHO Micronutrient Guidelines