Blood Tests for Vitamin B12 Deficiency
Vitamin B12 keeps nerves and red blood cells healthy. A shortage can cause tiredness, numbness or tingling in the hands and feet, memory and mood problems, and a type of anemia with large red blood cells. It is more common after 50, on a vegan diet, after weight-loss surgery, with pernicious anemia, and with long-term use of metformin or acid-reducing medicines. A B12 blood test is the place to start, but on its own it can miss a deficiency: results in the low-normal range are common in people whose cells are short of B12. Methylmalonic acid (MMA) and homocysteine rise when the body lacks B12, so they show whether a borderline result matters. With JustLabs, you can order these tests online at transparent cash prices, with no doctor visit or insurance required.
Recommended Tests
Includes all 5 recommended tests below.
All 5 recommended tests
$84 + one $18 order fee = $102 all-in
If B12 is low without an obvious cause, intrinsic factor and parietal cell antibodies check for pernicious anemia, an autoimmune cause of poor B12 absorption.
$92 · 3 tests + $18 order fee per order
Why a B12 test alone can miss a deficiency
- B12 clearly low (under 200 pg/mL)
- Deficiency is likely. The next question for your clinician is why: diet, absorption, pernicious anemia or a medicine.
- B12 borderline (about 200–300 pg/mL)
- The gray zone. A high MMA, and often a high homocysteine, shows the body is short of B12 despite a normal-looking number.
- B12 normal but symptoms persist
- MMA and homocysteine can still be raised. Folate and the CBC check for a related deficiency and for anemia.
- Taking B12 or folic acid already
- Supplements raise blood levels and can mask a problem. Folic acid can correct the anemia while nerve damage from low B12 continues, so tell your clinician what you take.
Understanding Your Results
| Test | Normal Range | Low Means | High Means |
|---|---|---|---|
| Vitamin B12 | Above about 300 pg/mL is generally adequate | Under 200 pg/mL is deficient; 200–300 is borderline and worth an MMA test | Usually from supplements or injections |
| Methylmalonic acid (MMA) | Within the range on your report | B12 is likely adequate at the cell level | Supports B12 deficiency, even with a normal B12 (kidney disease can also raise it) |
| Homocysteine | Within the range on your report | B12 and folate likely adequate | Low B12 or folate, kidney disease, or genetics; not specific to B12 |
| Folate | Within the range on your report | Folate deficiency, which causes the same anemia as low B12 | Usually from supplements or fortified foods |
| MCV (in the CBC) | About 80–100 fL | Small red cells, more typical of iron deficiency | Large red cells, seen with low B12 or folate |
How to Order
Order Online
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Get Results
B12, folate and the CBC usually post within 1-2 business days; homocysteine and MMA take longer, about 3-5 business days.
Frequently Asked Questions
Related Conditions
Content reviewed for accuracy by the JustLabs editorial team.