Abstract
Vitamin B12 testing is recommended for individuals with clinical signs and symptoms suggestive of B12 deficiency, and when there is reasonable clinical suspicion of deficiency due to risk factors (e.g. inadequate dietary intake, malabsorptive conditions). Where vitamin B12 testing is indicated, total serum B12 is typically the first-line test. Active B12 may be requested if total B12 results are indeterminate, or during pregnancy. If total or active B12 tests are inconclusive, methylmalonic acid or homocysteine testing may be considered; however, their concentrations may be elevated in other conditions. In individuals with confirmed B12 deficiency, B12 supplementation is required, with the choice of formulation, duration and dosage guided by the underlying cause and severity of the deficiency and patient preference.