Pseudohyperkalaemia in essential thrombocytosis: an important clinical reminder

SUMMARY: An 82-year-old female was admitted to a general hospital due to progressive bilateral lower limb weakness. A T8–T9 extramedullary meningioma was diagnosed by MRI, and the patient was referred for excision of the tumour. During the patient’s admission, she was noted to have persistent hyperkalaemia which was refractory to treatment. Following a review by an endocrinology team, a diagnosis of pseudohyperkalaemia secondary to thrombocytosis was made. This case demonstrates the importance of promptly identifying patients who are susceptible to pseudohyperkalaemia, in order to prevent its potentially serious consequences. LEARNING POINTS: Pseudohyperkalaemia should be considered in patients with unexplained or asymptomatic hyperkalaemia. It should also be considered in those patients who are resistant to the classical treatment of hyperkalaemia. A diagnosis of pseudohyperkalaemia is considered when there is a difference of >0.4 mmol/L of potassium between serum and plasma potassium in the absence of symptoms and ECG changes. In patients who are presenting with consistently elevated serum potassium levels, it may be beneficial to take venous blood gas and/ or plasma potassium levels to rule out pseudohyperkalaemia. Pseudohyperkalaemia may subject patients to iatrogenic hypokalaemia which can be potentially fatal. Pseudohyperkalaemia can occur secondary to thrombocytosis, red cell haemolysis due to improper blood letting techniques, leukaemia and lymphoma.