In brief
Blood tests for vitamin B12 and folate, usually ordered after a full blood count shows a problem, or for nerve symptoms.
What it measures
Total vitamin B12 and serum folate are the first tests. Active B12 (holotranscobalamin) has also been available as a first-line test since July 2025. Red blood cell folate testing is no longer used.
Why it is done
To look for a deficiency, usually after abnormal full blood count results, and sometimes when there are nerve symptoms.
Reading the results
- Low levels mean a deficiency, and further tests are needed to find the cause.
- Results can be normal even with a deficiency, more often when iron deficiency is also present.
- People at higher risk of low B12 include strict vegetarians and vegans after many years, older people, people with pernicious anaemia, and people taking metformin or proton pump inhibitors.
Medicare provides a rebate for a total vitamin B12 test once every 12 months.
Before the test
Ask your doctor for instructions. You may be asked to fast, especially for serum folate, and biotin supplements can interfere with testing.
What can affect the result
- Biotin supplements
- Recent food (for serum folate)
- Iron deficiency
Related topics
Connections
Vitamin B12 and folate tests measures
Active B12 is considered the best measure of B12 in the body.
Total vitamin B12 and serum folate are the first tests used to look for a deficiency.
Sources
Test information summarised from the sources listed on this page, read on 19 October 2026. General education only, not medical advice. Spotted a mistake? Please tell us through the HuBu-Intel contact page.