Active Vitamin B12

The fraction of vitamin B12 your cells can actually use. It falls before total B12 does, so it picks up a developing deficiency earlier.

Active Vitamin B12 in the Biomarker Guide — what it is, why it is tested, and what moves the number.

Add-on markers can only be added to venous samples.

Timing

No fasting needed and no particular time of day. If you take a B12 supplement or have had a B12 injection, the result reflects that rather than your own stores.

Turnaround: the lab reports this test within 24 hours of receiving your sample, counted in working days. Most samples reach them within about 3 days of posting. Full detail on our Turnaround Times page.

We do not interpret results. Not medical advice or a diagnosis.