Determinazione della vitamina B12 nel siero: Indicazioni per la richiesta e l'interpretazione dei risultati = Determination of vitamin B12in serum: Recommendations for test request and result interpretation

The measurement of vitamin B12 (B12) in serum has an overall poor capability to rule out subjects for B12 deficiency. Furthermore, trying to identify those subjects by resorting to one solely test threshold level (e.g., the lower reference limit) may mislead the clinical diagnosis. Clinical laboratories should therefore optimize the test interpretation by replacing in their report the standard reference interval with a categorization of risk for B12 deficiency. Accordingly, a B12 concentration <100 ng/L may indicate a probable B12 deficiency and the need for vitamin supplementation. A possible or unlikely deficiency may be associated with marker results, respectively, below and above 300 ng/L. Finally, in subjects with B12 concentrations >400 ng/L, the vitamin deficiency may be excluded. Hemodialysis patients and pregnant woman have emerged as a target for B12 testing, although cost-effectiveness evaluations are difficult to perform in absence of reliable literature data. Monitoring B12 concentrations in serum to evaluate the effectiveness of B12 supplementation is not clinically useful.