Vitamin B12 Deficiency
Diagnosis
Offer an initial diagnostic test for vitamin B12 deficiency to people who have:
- at least 1 common symptom or sign (see box 1) and
- at least 1 common risk factor for the condition (see box 2).
Use clinical judgement when deciding whether to test people who have at least 1
common symptom or sign (see box 1) but no common risk factors (see box 2).
Use either total B12 (serum cobalamin) or active B12 (serum holotranscobalamin)
as the initial test for suspected vitamin B12 deficiency unless:
- the test needs to be done during pregnancy, or
- recreational nitrous oxide use is the suspected cause of deficiency.
Use active B12 as the initial test for suspected vitamin B12 deficiency during
pregnancy.
If the person has suspected vitamin B12 deficiency caused by recreational use of
nitrous oxide:
- use plasma homocysteine or serum methylmalonic acid (MMA) as the initial
test and
- if using plasma homocysteine, refer the person to phlebotomy services in
secondary care for this test.
Take blood samples for diagnostic tests before starting vitamin B12 replacement.