Case Presentation: A 45-year-old man with hypertension, hyperlipidemia, prior subdural hematoma s/p craniotomy, and alcohol use disorder presented with progressive weakness, somnolence, and visual changes. He denied cardiac, respiratory, or gastrointestinal symptoms. Laboratory evaluation revealed a white blood cell count of 402,000/µL with 77% circulating blasts, hemoglobin 8.6 g/dL, and platelets 42,000/µL. Venous potassium was critically low at 1.7 mmol/L, confirmed on repeat testing. Creatinine was 2.48 mg/dL, and LDH was 2,386 U/L, consistent with acute kidney injury and high cellular turnover. Despite severe hypokalemia, electrocardiogram showed normal T waves without U waves.Given the discordance between the lab value and clinical findings, a point-of-care (POC) potassium measurement was obtained, revealing a level of 3.0 mmol/L. Peripheral smear confirmed acute myeloid leukemia (AML), and the patient underwent leukapheresis followed by induction chemotherapy with cytarabine. Within six hours, repeat potassium levels rose to 5.3–5.8 mmol/L due to tumor lysis syndrome (TLS), necessitating emergent management for hyperkalemia.
Discussion: Spurious hypokalemia occurs in hematologic malignancies, most often when leukocyte counts exceed 100,000/µL. The mechanism involves ongoing potassium uptake by leukemic blasts in vitro, particularly in samples that are not rapidly processed or are kept at room temperature. This artifact can lead to misdiagnosis and inappropriate potassium supplementation. In this patient, the lack of electrocardiographic abnormalities and the discrepancy between the lab and POC results suggested a laboratory artifact rather than true hypokalemia. Recognizing this distinction is critical, as aggressive potassium replacement in such patients can lead to rebound hyperkalemia, especially in the setting of TLS, when intracellular potassium is released into circulation following cytotoxic therapy.
Conclusions: Spurious hypokalemia should be suspected in patients with extreme leukocytosis and unexpectedly low serum potassium, particularly when clinical and electrocardiographic findings are incongruent. Point-of-care testing provides a rapid and reliable assessment of true potassium levels and can prevent iatrogenic harm. This case emphasizes the need for clinical judgment to ensure safe and accurate electrolyte management in patients with hematologic malignancies.