[Vitamin B12 in practice: When to test ? How to test ? And who should be treated?].

Vitamin B12 deficiency is common in outpatients and inpatient populations, with potentially severe neuropsychiatric and hematological impact, which requires timely diagnosis and treatment. The different diagnostic tests all have their limitations but can be combined, sequentially. We propose to review the treatment options according to the different etiologies of the deficiency, highlighting the costs of the therapies and their coverage by the health insurance.