[Pseudohyperkalemia: clinical chemistry for the clinician]

Hyperkalemia is an electrolyte disorder requiring medical attention because it can cause cardiac arrhythmias. Pseudohyperkalemia is the phenomenon of an elevated potassium concentration that is present in the blood sample but not in the patient. Pseudohyperkalemia can be caused by hemolysis, leukocytosis, thrombocytosis, seasonal pseudohyperkalemia, potassium release from muscle cells due to fist clenching during venipuncture, and contamination due to blood withdrawal from an intravenous line over which potassium was administered. Rarer causes include EDTA contamination and familial pseudohyperkalemia.A 23-year old woman was admitted with ascites due to polycythemia vera and essential thrombocytosis for which hydroxycarbamide was started. The reported serum potassium concentrations were 6.1 and 6.8 mmol/l. The use of spironolactone was discontinued and she was treated with sodium polystyrene sulfonate and insulin-glucose infusion. The serum potassium concentration only decreased on the ninth day of admission, when the thrombocyte count was normalizing. A diagnosis of pseudohyperkalemia due to thrombocytosis was established.Knowledge of the causes of pseudohyperkalemia and interaction between the clinician and clinical chemist aids in the differentiation between true hyperkalemia and pseudohyperkalemia and may prevent unnecessary diagnostics and harmful treatment.