Abstract
Hyperkalaemia is a relatively common medical emergency that necessitates prompt and urgent intervention. There is an ongoing debate over the precise threshold for treating hyperkalaemia due to variability in clinical scenarios. This case report highlights the need to differentiate true hyperkalaemia from pseudohyperkalaemia by analysing serum and plasma potassium levels, thus avoiding unnecessary treatment and the risk of iatrogenic hypokalemia. This case report discusses an 89-year-old male who presented with recurrent falls and fluctuating serum potassium levels but showed no symptoms of hyperkalaemia and had no relevant drug history. Further investigation revealed an underlying myeloproliferative neoplasm with thrombocytosis, leading to the diagnosis of pseudohyperkalaemia, reflected by a significant discrepancy between serum and plasma potassium levels, showcasing the importance of considering pseudohyperkalaemia in patients with haematological malignancies and thrombocytosis.