Introduction Cobalamin plays an essential role in haematopoiesis, cell metabolism, production of DNA and neuronal function. High serum concentration of cobalamin is a common but underestimated finding. The aetiology of hypercobalaminaemia includes excess vitamin B12 intake, solid neoplasms, haematological malignancies, liver disease, renal failure and autoimmune diseases. Paradoxically, hypercobalaminaemia can be associated with a functional B12 deficiency. A finding of high serum cobalamin should prompt an early and in-depth search for these entities to ensure a favourable prognosis. Case presentation We present a case of a thirteen-year old girl who presented with non-specific symptoms and an incidental finding of a raised serum cobalamin (1400 pg/mL) with initially only minor full blood count (FBC) abnormalities. Upon her assessment in the haematology clinic in OLCHC, repeat FBC results showed progressive anaemia with macrocytosis, a falling platelet count and serum cobalamin concentration of >6000 pg/mL. On repeat the cobalamin had increased to 10926 pg/mL. Urinary methylmalonic acid, plasma total homocysteine, liver and renal function were unremarkable, and she was not taking supplements or oestrogens. A bone marrow aspirate showed findings consistent with early diagnosis of Acute Myeloid Leukaemia (AML). Conclusion This case highlights the importance of hypercobalaminaemia which should be followed by the search for the cause of this finding as early diagnosis can be an important prognostic factor. A possible malignant blood disorder should be considered when serum cobalamin concentrations are above the reference range and where increases due to supplements, inflammatory, renal or liver disease have been excluded. This underscores the importance of laboratories offering numerical values (rather than reporting high results as greater than a cut-off value) for elevated vitamin B12 levels in cases with minor but progressive FBC changes. An increase in the level of B12 may indicate the need for prompt referral to a haematologist for assessment and monitoring.
