Severe hyperkalaemia with normal electrocardiogram.

Elevated serum potassium without associated electrocardiograph and biochemical changes makes the diagnosis of pseudohyperkalaemia likely. One of the common causes of this is thrombocytosis with in vitro leak of cellular potassium due to increased fragility of the platelets. We report a case where the diagnosis of essential thrombocytosis was made during investigation of persistent hyperkalaemia in an apparently healthy female.