Measures active vitamin B12 — the fraction of B12 that’s actually available for the body to use — giving a more precise picture than a standard B12 test.
About this test
Active B12 measures the portion of vitamin B12 that is available for the body to use. This can sometimes provide more specific information than a total B12 measurement. The test may be useful when investigating fatigue, weakness, numbness, tingling, or possible nutritional deficiency. It can help a clinician decide whether further B12 assessment or treatment may be appropriate. Results should be interpreted alongside symptoms, blood count, diet, medication, and other nutrient tests. No special preparation is usually required.
What’s included1 marker
- Vitamin B12 – active
What to expect
Before your test
Drink plenty of water beforehand. It makes the blood draw easier.
Some tests need you to fast for at least 12 hours, with water only. If you're not sure about yours, ask us before your appointment.
Stop oral and IV vitamin supplements 24 hours before your test, as they can affect some results. Keep taking your regular prescribed medication unless your GP tells you otherwise. Some types of hormonal contraception can affect results, so mention it to us.
At your appointment
You'll fill in a short medical questionnaire first. We'll also check your blood pressure, heart rate and blood oxygen level. A healthcare professional then takes your sample from a vein at our clinic. The visit takes about 15 minutes.
A cold numbing spray is available if you'd like one. If you feel nervous, tell us and we'll help you feel at ease.
Your results
Results usually take 3 to 7 working days. We can't guarantee this, because some things are outside our control. A doctor reviews your results and adds recommendations to your report. We email the report to you as a PDF.
If there's a problem with your sample, we may ask you to come back for another blood draw.
After your test
You don't need any recovery time. Keep the dressing on for 30 minutes and keep it clean and dry.
Who can have a blood test?
Blood tests are for people aged 18 and over. You don't need a GP referral letter. Please book tests for yourself only.
Appointments are available Monday to Saturday.
Are the laboratories accredited?
Your sample is analysed in a laboratory that is CQC-registered and accredited by UKAS.
A blood test gives you information. It isn't a diagnosis. If you have symptoms or you're worried about your health, speak to your GP.