A test that measures the level of vitamin B12 in the blood. It is used in the evaluation of anemia, neurological symptoms and nutritional/absorption problems.
Indication
- Investigation of fatigue, pallor and macrocytic anemia
- Neurological symptoms such as numbness, tingling or balance disturbance in the hands and feet
- Evaluation of cognitive slowing, memory complaints or depressive symptoms
- Routine screening in vegetarians and vegans
- B12 deficiency screening in elderly individuals
- Follow-up after gastric surgery (e.g. sleeve gastrectomy, gastric bypass)
- Suspicion of pernicious anemia and atrophic gastritis
- Monitoring of long-term proton pump inhibitor, metformin or H2 blocker use
Preparation
- Fasting is generally not required; if other tests are requested from the same sample, follow the physician's recommendation
- B12 supplements and B12-containing vitamins should be discontinued at least 24 hours (preferably 48 hours) in advance
- All medications used (especially metformin and PPIs) should be reported to the physician
- If a B12 injection has recently been administered, this should be reported, as the result will naturally appear high
How it's performed
- A venous blood sample is taken from the arm (usually 2-3 mL)
- Blood is collected in a biochemistry tube
- B12 level is measured on automated analyzers using chemiluminescence or immunoassay methods
- The result is reported in pg/mL or pmol/L
- In borderline values, further evaluation can be performed with metabolic markers such as methylmalonic acid and homocysteine
Post-procedure
- Results are usually available the same day or the next business day
- If low B12 is detected, further evaluation for the cause (nutrition, absorption, autoimmune gastritis) is planned
- Treatment options: high-dose oral B12 or intramuscular B12 injection (usually a loading and then maintenance schedule)
- Follow-up B12 and, when needed, complete blood count are reassessed 1-3 months after treatment is started
- In absorption problems such as pernicious anemia, lifelong B12 treatment is generally required
Risks
- Transient pain or bruising at the venipuncture site
- Rare small hematoma
- Dizziness from a vasovagal reaction (rare)
- Very rarely, local infection at the needle site
FAQ
What is the normal value of B12?
In most laboratories, levels below 200 pg/mL are considered deficient and 200-300 pg/mL is borderline; if clinical symptoms are present, confirmation with methylmalonic acid is recommended even within this range. Upper limits vary by laboratory.
Is oral B12 or injection more effective?
In most deficiencies, high-dose oral B12 (1000 mcg/day) can be effective. In pernicious anemia, absorption disorders or severe neurological symptoms, intramuscular injection is preferred initially; the regimen is individualized.
I have a borderline B12 level — are additional tests needed?
In borderline values, methylmalonic acid and homocysteine tests, which reflect actual tissue status, can confirm the diagnosis. Clinical symptoms also guide the treatment decision.
What are the symptoms of B12 deficiency?
Symptoms can include fatigue, pallor, burning tongue, numbness or tingling in hands and feet, balance problems, and difficulty with memory and concentration. Untreated deficiency may cause permanent nerve damage.
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