Severe Hyperkalemia With a Normal Electrocardiogram: Pseudohyperkalemia in Extreme Leukocytosis

Pseudohyperkalemia is an important laboratory artifact that may lead to unnecessary and potentially harmful treatment if not recognized promptly. We report a case of apparent severe hyperkalemia in a patient with extreme leukocytosis, in whom repeated serum potassium measurements remained markedly elevated despite the absence of clinical symptoms or electrocardiographic abnormalities. Given the discordance between biochemical findings and clinical presentation, further evaluation was undertaken using point-of-care whole blood analysis, which demonstrated a normal potassium level. The discrepancy was consistent with pseudohyperkalemia due to in vitro leukocyte lysis during sample processing. Recognition of this phenomenon prevented inappropriate potassium-lowering therapy. This case highlights the importance of correlating laboratory results with the clinical picture and emphasizes the value of alternative testing modalities in resolving diagnostic uncertainty.