Abstract
BACKGROUND: Discordant Vitamin B12 results can result from immunoassay interferences, potentially leading to unnecessary diagnostic procedures and misdiagnoses if not properly recognized. CASE PRESENTATION: A 76-year-old male with a history of IgA nephropathy, hypertension, and other comorbidities presented with unexpectedly elevated total Vitamin B12 levels despite no supplement use and normal hematological and biochemical parameters. Polyethylene glycol (PEG) precipitation demonstrated markedly reduced recovery, indicating the presence of macro-VitB12. Pretreatment with blocking reagents and exclusion of heterophilic antibodies confirmed the interference. The discrepancy observed between analytical platforms further supported this finding. CONCLUSION: Vitamin B12 results should always be interpreted in conjunction with clinical findings. Polyethylene glycol (PEG) precipitation is a cost-effective and accessible method for detecting macro-VitB12, particularly in cases where analytical results are inconsistent with the clinical presentation.