Vitamin B12 and folate
Also known as: cobalamin test, folic acid test, B12 and folate blood test
Two blood tests, usually ordered together, for the vitamins the bone marrow needs to make normal red cells and the nervous system needs to keep nerves working. Deficiency of either causes anaemia with large red cells; vitamin B12 deficiency can also damage nerves, sometimes before the blood count changes.
- Abbreviations
- B12
- Kind
- Laboratory test
- Categories
- Vitamins, minerals & nutrition, Blood & haematology
- Specimen
- Serum
- Method
- Immunoassay
- Terminology
- LOINC 2132-9, 2284-8
- Type
- Blood test
- Sample
- Blood from a vein
- Used for
- Investigating anaemia with large red cells, nerve symptoms, and monitoring people on long-term metformin
- Measures
- The blood levels of vitamin B12 and folate
- Result
- Numeric, read against the laboratory's intervals with a borderline zone for B12
Why is it used?
- Anaemia with large red cells (a high MCV)
- Numbness, tingling, balance problems or memory change that could be B12 deficiency
- Tiredness, a sore tongue or mouth ulcers
- Long-term metformin or acid-suppressing treatment, which can lower B12
- Before and during pregnancy planning, for folate
What does it measure?
| Component | What it measures | A higher value may be seen in | A lower value may be seen in |
|---|---|---|---|
| Vitamin B12 | Serum cobalamin | Supplements, liver disease | Pernicious anaemia, diet, malabsorption, metformin |
| Folate | Serum (or red cell) folate | Supplements, recent meal | Diet, alcohol, malabsorption, pregnancy, methotrexate |
A high or low value can be associated with several different situations; the result is interpreted with other results, symptoms, history and clinical findings.
How is it performed?
A venous blood sample.
Specimen. Venous blood (serum)
Do I need to prepare?
None usually; the laboratory may ask for a fasting sample. Say if you take B12 or folic acid supplements, or have had a B12 injection, which mask deficiency.
What do the results generally mean?
| Finding | What it may indicate |
|---|---|
| Low vitamin B12 | Deficiency, whose cause (pernicious anaemia, diet, absorption, medicines) is then sought; further tests such as intrinsic-factor antibodies may follow |
| Borderline vitamin B12 | An indeterminate zone in which symptoms, the blood count and sometimes additional markers decide whether treatment is given |
| Low folate | Deficiency from diet, alcohol, malabsorption, pregnancy or a medicine; treated after B12 status is known, because folic acid alone can worsen the nerve damage of untreated B12 deficiency |
| Both normal with a high MCV | Other causes of large red cells are considered: alcohol, liver disease, thyroid disease, some medicines, bone-marrow disorders |
What can affect the result?
- Supplements, injections and fortified foods, which raise the results
- Metformin, proton-pump inhibitors and H2 blockers, which lower B12 over years
- Pregnancy and oral contraceptives, which lower measured B12
- Recent meals, which raise serum folate
- Liver disease and some blood disorders, which raise B12 without reflecting stores
Medicines. Metformin, proton-pump inhibitors, H2 blockers and colchicine can lower B12; methotrexate, some antiepileptics and trimethoprim interfere with folate.
What can the test not tell you?
- Whether nerve damage from B12 deficiency will recover
- The cause of a low result without further tests
- Tissue B12 status precisely: the blood level is an imperfect proxy
Serum B12 has a wide indeterminate range and can be falsely normal in people with intrinsic-factor antibodies; serum folate reflects recent intake more than stores. Treatment is often started on clinical grounds when a result is borderline.
Other tests commonly used with it
Catalogued concepts this page covers
Concepts of the master test taxonomy that resolve to this page; each links to its category.