Vitamin B12 Test
Also known as: Cobalamin, B12, Cyanocobalamin
What is Vitamin B12?
Vitamin B12 is essential for nerve function, red blood cell formation, and DNA synthesis. It is found in animal products and fortified foods.[MedlinePlus (NIH)]
What This Test Measures
This test measures the level of vitamin B12 in your blood. Deficiency can cause anemia and neurological problems.[Mayo Clinic]
Why It's Important
B12 deficiency causes macrocytic anemia and can lead to irreversible nerve damage if untreated.[MedlinePlus (NIH)]
People at risk include vegans, older adults, those with pernicious anemia, and people with GI disorders.[Cleveland Clinic]
Who Should Get This Test?
Vitamin B12 testing is important for people at risk of deficiency.
Risk Factors
- Vegans and vegetarians (B12 found only in animal products)
- Adults over 50 (decreased absorption)
- People with pernicious anemia or atrophic gastritis
- History of gastrointestinal surgery (gastric bypass, bowel resection)
- Crohn's disease, celiac disease, or other malabsorption disorders
- Taking metformin for diabetes
- Taking proton pump inhibitors (PPIs) or H2 blockers long-term
- Chronic alcoholism
- Symptoms of deficiency: fatigue, weakness, numbness/tingling, memory problems
- Macrocytic anemia found on CBC
Screening Schedule
Routine screening is not recommended for most people. Test when deficiency is suspected or for high-risk groups.
What Happens During the Test
A blood sample is drawn from a vein, usually in the arm. The test measures total serum B12 levels.
Duration
5 minutes for the blood draw; results usually available within 1-2 days
Discomfort Level
Minimal - brief pinch from needle insertion
Risks & Side Effects
Vitamin B12 testing through blood draw carries very few risks.
- •Minor pain or bruising at the needle site
- •Slight bleeding
- •Rarely, lightheadedness
- •Very rare risk of infection
Normal Range
200 to 900 pg/mL.
Note: Some experts consider levels below 300 pg/mL borderline low.
Source: MedlinePlus (NIH)Unit Conversion
Convert between pg/mL and pmol/L
| pg/mL | pmol/L |
|---|---|
| 150 | 111 |
| 200 | 148 |
| 300 | 221 |
| 400 | 295 |
| 500 | 369 |
| 700 | 517 |
| 900 | 664 |
| 1200 | 886 |
High Values
High B12 is usually not harmful and may be due to supplements, liver disease, or certain blood cancers.[Cleveland Clinic]
Low Values
Low B12 causes fatigue, weakness, anemia, numbness/tingling, memory problems, and difficulty walking. Causes include poor diet, malabsorption, and pernicious anemia.[Mayo Clinic]
Test Limitations & Accuracy
Serum B12 levels do not always reflect true tissue deficiency.
- ⚠Normal serum B12 can occur with functional deficiency at the cellular level
- ⚠High folate intake can mask B12 deficiency symptoms
- ⚠Supplements taken before testing will elevate results
- ⚠Recent B12 injections will affect results
- ⚠Oral contraceptives may lower measured levels without true deficiency
- ⚠Pregnancy can lower B12 levels physiologically
- ⚠Kidney disease and liver disease can affect levels
- ⚠Does not distinguish between active and inactive forms of B12
Alternative & Complementary Tests
Additional tests can better assess B12 status when results are borderline.
Most sensitive marker - elevated in B12 deficiency even with normal serum B12
Elevated in both B12 and folate deficiency
Measures the biologically active form of B12
To check for macrocytic anemia (large red blood cells)
Often checked together as both cause similar anemia
To diagnose pernicious anemia
Frequently Asked Questions
What foods are high in vitamin B12?
B12 is found naturally in animal products: meat, fish, poultry, eggs, and dairy. Vegans should consume fortified foods or supplements.
Source: MedlinePlus (NIH)References
Related Condition Guides
Medical Disclaimer
This information is for educational purposes only and is not intended as medical advice. Always consult with a qualified healthcare provider for interpretation of test results and medical decisions.
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