Hypervitaminosis B12: an indicator of potential significant morbidity.

A woman in her 60s with a history of vitamin B12 deficiency treated with intramuscular hydroxocobalamin was attending a specialist clinic for the management of persisting breathlessness following a previous pulmonary embolism. She reported that a persistently elevated vitamin B12 had been identified several months previously, despite the withdrawal of replacement therapy, and that the cause could not be explained to her by her general practitioner. Recognition of the potentially serious implications of this finding led to the identification of a pancreatic tumour which, by the time of diagnosis, had become too advanced for active management. We describe the metabolism of vitamin B12 in the context of hypervitaminosis B12 as a reflection of elevated transcobalamin consequent to underlying disease and the need to identify promptly the underlying cause.