Pseudohyperkalaemia - a cause of diagnostic confusion.

Marked hyperkalaemia occurred on more than one occasion in 3 patients with thrombocytosis caused by the myeloproliferative syndrome. Initial failure to recognize that the elevation in the serum potassium level was an artefact resulted in unnecessary admissions to hospital and inappropriate investigations and treatment. Awareness of this entity and the use of suitable confirmatory tests should avoid such problems in management.