Severe hyperkalaemia with normal electrocardiogram

Elevated serum potassium without associated electrocardiograph and biochemi cal changes makes the diagnosis of pseudohyperkalaemia likely. One of the c ommon causes of this is thrombocytosis with in vitro leak of cellular potas sium due to increased fragility of the platelets. We report a case where th e diagnosis of essential thrombocytosis was made during investigation of pe rsistent hyperkalaemia in an apparently healthy female.