Unrecognized pseudohyperkalaemia in essential thrombocythaemia

A 99-year-old woman was admitted following a mechanical fall. The patient suffered from frequent falls averaging around six falls per year. On this occasion the patient explained that she had simply lost her balance and denied any further symptoms. The patient’s past medical history was significant for essential thrombocythaemia diagnosed 10 years earlier which was initially managed with hydroxycarbamide and followed up via outpatient haematology clinics. In addition to this the patient also had a history of macular degeneration, carpal tunnel syndrome and cognitive impairment. Blood tests on admission showed a platelet count of 1836 with a potassium concentration of 5.9 mmol/L. Repeat blood tests following admission demonstrated platelet count now of 2348 with a subsequent rise in potassium level to 6.9 mmol/L. There were curiously no ECG changes of hyperkalaemia and the rest of the blood results, including renal function and inflammatory markers were normal. Nonetheless the patient was infused with insulin and dextrose which brought the potassium level to 5.6 mmol/L. However the potassium level was difficult to control and continued to consistently rise beyond 6 mmol/L. The patient was subsequently repeatedly treated with insulin and dextrose infusions to lower the potassium level several times. After exhausting the causes of high serum potassium levels a plasma potassium was requested from the laboratory. The result returned as 3.0 mmol/L. The patient was in fact hypokalaemic secondary to repeated insulin dextrose infusions. The diagnosis of pseudohyperkalaemia due to thrombocythaemia was made and only plasma potassium levels were recorded subsequently.