TempoLife › Features › Blood test reference ranges › vitamin-b12
Vitamin B12
The total vitamin B12 carried in the blood, most of which is bound to a protein that cells cannot use. That is the test's main weakness: the total can look adequate while the usable fraction is not, which is why methylmalonic acid or active B12 is sometimes measured when the picture does not fit.
General information only — not a diagnosis, not treatment and not a substitute for your doctor. Reference ranges differ between laboratories, so the range printed on your own report is the one that counts, and only a clinician who knows your history can say what a result means for you. Never start, stop or change a medicine or supplement based on this page.
Usual adult reference range
The ranges below are typical adult reference intervals. Your own laboratory sets its own, printed next to your result, and that is the one to compare against.
| Group | SI units (pmol/L) | Conventional (ng/L (pg/mL)) |
|---|---|---|
| Typical adult reference interval | 148-650 | 200-900 |
| Commonly used deficiency threshold | below 148 | below 200 |
Source: Typical adult reference interval published by clinical laboratories; deficiency thresholds differ between assays and guidelines. · checked 2026-09-02
What a high result generally indicates
A high B12 is usually just supplementation, including injections given weeks earlier. Unexplained high levels without supplements are occasionally investigated, because liver disease and some blood disorders raise it.
What a low result generally indicates
Low B12 causes anaemia with large red cells and, importantly, neurological symptoms — numbness, tingling, unsteadiness, memory change — which can appear before the blood count changes. Causes include a diet with no animal foods, pernicious anaemia, gastric or ileal surgery, and long-term metformin or acid-suppressing treatment.
These are general patterns, not a diagnosis. Many things cause a high or low result, and the same figure means different things in different people. What yours means is a question for the doctor who ordered the test.
What affects this result
- A diet containing no animal foods, over a period of years.
- Metformin lowers absorption over long-term use.
- Proton pump inhibitors and H2 blockers reduce absorption from food.
- Pernicious anaemia — an autoimmune loss of intrinsic factor.
- Gastric or small-bowel surgery.
- Recent supplements or injections raise the measured level regardless of stores.
Before the test
No fasting needed. Tell the requester about any B12 supplement or injection — it changes how the result reads.
Any preparation instruction that comes with your test slip overrides this general note — follow the one your clinician or laboratory gave you.
The one thing to take from this page
The range above is a typical interval for orientation. Your own laboratory's range, printed beside your result, is the one that applies to you — and a result is only meaningful alongside your symptoms, your history, your medicines and your other tests. That reading is a clinician's job. This page cannot diagnose anything, cannot tell you to change a medicine or a supplement, and is not a substitute for the person who ordered your test.
Frequently asked questions
What is the normal range for vitamin b12?
A typical adult reference interval is 148–650 pmol/L, but laboratories differ — the range printed on your own report is the one to use. And a result inside or outside a range is only meaningful in context, which is your doctor's reading, not a web page's.
What does a high vitamin b12 mean?
A high B12 is usually just supplementation, including injections given weeks earlier. Unexplained high levels without supplements are occasionally investigated, because liver disease and some blood disorders raise it.
What does a low vitamin b12 mean?
Low B12 causes anaemia with large red cells and, importantly, neurological symptoms — numbness, tingling, unsteadiness, memory change — which can appear before the blood count changes. Causes include a diet with no animal foods, pernicious anaemia, gastric or ileal surgery, and long-term metformin or acid-suppressing treatment.
Other markers
Haemoglobin
Hb, HGB
Ferritin
Serum ferritin
Vitamin D (25-OH)
25-hydroxyvitamin D, calcidiol
HbA1c
Glycated haemoglobin, A1c
Fasting glucose
Fasting plasma glucose, FPG
Total cholesterol
TC
All markers and the checker · Symptoms and nutrients · Medicine interactions
Bring context to your next result
TempoLife tracks the weight, sleep and activity trends a single blood test cannot see, so you and your doctor have the fuller picture.