What it measures
The test measures all the vitamin B12 in the blood, both the part bound to carrier proteins and the smaller active part. Most of it is bound to a carrier that cells cannot use, so a total result does not always show what cells can take up.
Why people test it
- Measured when tiredness, pins and needles, a sore tongue or anaemia raise the question of low B12.
- Checked in people more likely to run low, such as vegans, older adults and people taking metformin.
- Monitored in people having B12 injections or after stomach surgery.
- Checked by some endurance athletes, as B12 is needed to make red blood cells.
Typical range
Ranges vary by lab, method, age and sex, and your report shows the lab's own range. Labs report B12 in ng/L or pmol/L, so check the unit before comparing results.
Finger-prick or vein?
A finger-prick sample is usually fine, and vein draws are offered too.
