# Vitamin B12 and folate (B12)

Two vitamins for red cells and nerves; for people eating little animal food, on metformin, or over 50.

Type: lab · Unit: pmol/L (B12; pg/mL × 0.738), nmol/L (folate; ng/mL × 2.266) · Domain: Nutrition & Energy Balance · Accuracy: Laboratory · Importance: Recommended

Also called: vitamin B12 test, cobalamin, folic acid, folate test, active B12, holotranscobalamin, methylmalonic acid, MMA, vegan blood test

## In one sentence

Two vitamins the bone marrow needs to make red cells and the nerves need to keep their insulation; B12 comes only from animal foods or supplements, folate from leafy greens, legumes and fortified flour.

## Why it matters

A shortfall of either enlarges the red cells (a rising MCV on the blood count) and eventually causes anemia, and a B12 shortfall can damage nerves before the blood count changes at all, which is why the test is read with the blood count and not after it. The British haematology guideline is candid that there is no gold-standard test: serum B12 is first-line, methylmalonic acid is the second-line test that clarifies a borderline result, holotranscobalamin (active B12) could become first-line but keeps a grey zone of its own, definitive cut-offs are not possible across methods, and serum folate is as good as red cell folate and is the first-line test for folate (Devalia 2014). Three groups the panel names: people eating little or no animal food (in a review of 18 studies using the second-line markers, B12 depletion or deficiency was found in every vegetarian group studied, more often in vegans and in lifelong vegetarians; Pawlak 2013); people taking metformin (in a randomized trial of 390 people over 4.3 years, metformin lowered B12 by 19 percent and raised the absolute rate of deficiency below 150 pmol/L by 7.2 percentage points, one extra case for every 14 people treated; de Jager 2010); and people over 50, in whom the stomach's ability to free B12 from food falls.

## What moves it

B12 down: a diet without animal foods, metformin, the acid-suppressing medicines, age, gut conditions and gut surgery, pregnancy. Folate down: a diet short of greens and legumes, alcohol, some medicines, pregnancy. Both up, for weeks: a supplement, so that a tablet taken the morning of the draw measures the tablet, not you. Folate also rises for hours after a meal.

## How to measure it well

On the morning draw with the panel, fasting, so the folate is not reading breakfast. No high-dose B12 or folate supplement within 72 hours, and record what you take. Ask for pmol/L for B12 and nmol/L for folate, the New Zealand units; VT converts pg/mL and ng/mL. A borderline B12 (roughly 150 to 250 pmol/L) is a grey zone; the second-line tests that resolve it are the clinician's decision.

## How Vitality Tracker uses it

Stored as reported with the laboratory's range and flag, never overridden; typical laboratory reference 170 to 600 pmol/L for B12 and above 7 nmol/L for folate. VT's working optimal (v0.1), beneath in smaller type and marked *working*: B12 above 300 pmol/L, folate above 20 nmol/L. MCV from the blood count is read beside both; metformin on the medicine register shows the note from the trial above; the pre-draw line names high-dose B12 among the things that distort a result. Re-test yearly for the three groups the panel names, and six months after a supplement is started.

## How far to trust the number

Laboratory, with the guideline's caution: a serum B12 inside the range does not rule out a tissue shortfall, and one below it is not always one, which is what the second-line tests are for. Folate is more straightforward but moves with the last meal and the last drink.

## Method

No calculation. Conversions: B12 pg/mL × 0.738 = pmol/L; folate ng/mL × 2.266 = nmol/L.

## Sources

1. Devalia V, Hamilton MS, Molloy AM. Guidelines for the diagnosis and treatment of cobalamin and folate disorders. Br J Haematol 2014;166:496–513. [doi:10.1111/bjh.12959](https://doi.org/10.1111/bjh.12959)
2. Pawlak R, Parrott SJ, Raj S, Cullum-Dugan D, Lucus D. How prevalent is vitamin B12 deficiency among vegetarians? Nutr Rev 2013;71:110–7. [doi:10.1111/nure.12001](https://doi.org/10.1111/nure.12001)
3. de Jager J, et al. Long term treatment with metformin in patients with type 2 diabetes and risk of vitamin B-12 deficiency: randomised placebo controlled trial. BMJ 2010;340:c2181. [doi:10.1136/bmj.c2181](https://doi.org/10.1136/bmj.c2181)
4. Vitality Tracker, Recommended baseline lab panel v0.1; optimal set v0.1 (working).

## Related

- [Full blood count with differential](https://vitalitytracker.app/knowledge/full-blood-count)
- [Ferritin](https://vitalitytracker.app/knowledge/ferritin)
- [Supplements and medicines: log them as interventions](https://vitalitytracker.app/knowledge/supplements-and-medicines-as-interventions)
- [Getting your blood tests done in New Zealand](https://vitalitytracker.app/knowledge/blood-tests-in-new-zealand)

Reviewed October 2026 · v1

Source: https://vitalitytracker.app/knowledge/vitamin-b12-and-folate