Test library
B12 Blood Test
This blood test measures vitamin B12 (cobalamin) to check for deficiency. B12 is needed for healthy nerves and red blood cells, and low levels can occur with malabsorption, certain diets, or long-term medication use.
Order Vitamin B12 Deficiency Test
Order online and visit a local collection site, or choose an at-home kit where available. No referral and no insurance required.
Order Vitamin B12 Deficiency Test- Typical turnaround
- 1-3 business days
- Starting price
- From $35
- Results
- Confidential, online
Quick answer
The vitamin B12 test measures the amount of cobalamin in the blood. B12 is essential for normal nerve function and for producing healthy red blood cells. It is ordered when a deficiency is suspected because of diet, digestive conditions, or symptoms such as fatigue and tingling. The test uses a single blood sample, and a healthcare provider interprets the result with other findings.
What this test measures
Vitamin B12 is a water-soluble vitamin found naturally in animal foods, including meat, fish, eggs, and dairy. The body absorbs it with help from intrinsic factor, a protein made in the stomach, and stores a supply in the liver. Because of these stores, deficiency can take time to develop even when intake or absorption is poor.
The test measures serum cobalamin, and some laboratories add methylmalonic acid or homocysteine, which can become elevated when B12 is low. These secondary markers can be useful when the B12 result is borderline. A complete blood count may also be ordered to look for large red blood cells.
Risk factors for low B12 include a vegan diet without fortification, pernicious anemia, celiac disease, Crohn's disease, and some stomach or intestinal surgeries. Long-term use of certain medications can also reduce absorption. Testing helps a healthcare provider determine whether B12 is contributing to symptoms.
- Vitamin B12 (cobalamin)
- Methylmalonic acid
- Homocysteine
- Intrinsic factor antibodies
- Parietal cell antibodies
- Complete blood count with MCV when paired
- Serum folate when included
Why people order this test
- Evaluate fatigue, weakness, or tingling in the hands and feet
- Check B12 status on a vegan diet
- Investigate large red blood cells on a blood count
- Monitor absorption after stomach or intestinal surgery
- Assess long-term use of medications that reduce absorption
- Follow up on a previously borderline B12 result
How to prepare
Fasting is usually not required for a B12 test, but the laboratory may ask for it if other tests are included. A blood sample is collected from a vein, typically at the arm. Follow the instructions provided with the order.
Understanding your results
Results are typically reported within one to three business days. The report shows the B12 level and its reference range. A low result suggests deficiency, while a borderline result may prompt additional testing. A healthcare provider interprets the findings in context.
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Frequently Asked Questions
What does a vitamin B12 test measure?
It measures the level of cobalamin in the blood. Some laboratories also measure related markers such as methylmalonic acid or homocysteine.
What causes low vitamin B12?
Causes include a diet without animal products or fortification, malabsorption conditions, certain surgeries, and long-term use of some medications. A healthcare provider evaluates the likely cause.
Can a B12 test be normal even if I have a deficiency?
It is possible for standard B12 levels to look normal while tissue levels are low. Additional markers such as methylmalonic acid can help clarify the picture.
Do I need to fast before this test?
Fasting is usually not required unless the test is combined with others that call for it.
How often should B12 be checked?
The right interval depends on the person and the underlying reason for testing. A healthcare provider can recommend a schedule.
Ready to get tested?
Order online and visit a collection site near you, or choose a mail-in kit. No referral and no insurance required.
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