Case Presentation: Hyperkalemia is common in patients with hematological malignancies due to tumor lysis syndrome (TLS). Hyperkalemia can be further complicated by presence of pseudo-hyperkalemia in these patients. Accurate potassium measurement is critical as over-correction in the setting of hyperkalemia can lead to iatrogenic hypokalemia. A 38-year-old male presented to the Emergency Department for fatigue, weakness and weight loss for four weeks. On exam, he had splenomegaly and painless cervical lymphadenopathy. His white cell count was 193,000 and he was subsequently diagnosed with T cell ALL with flow cytometry. He was started on dexamethasone for cytoreduction with plan for a bone marrow biopsy. His uric acid levels were elevated at 9.5 mg/dl and there was concern for TLS, due to which the patient was put on allopurinol. The next morning, his potassium levels were 6.7 and his EKG showed peaked T waves, after which he was given calcium gluconate, insulin and furosemide. A few hours later, his potassium increased to 7.6, but his EKG changes had already resolved. A bedside point-of-care potassium level was found to be 3.1. Due to discrepancies in potassium levels, a suspicion of pseudo-hyperkalemia due to cell fragility arose; therefore, subsequently, potassium was collected in arterial blood gas (ABG) syringes, walked to the lab, and was then compared to the potassium collected in regular vacutainer vials which was transported via pneumatic chutes. The potassium level collected in ABG syringe later that day was 4.3 and that collected in the normal vacutainer vial was 5.5, thus confirming our suspicion.
Discussion: Pseudo-hyperkalemia can be seen in white blood cell neoplasms due to increased membrane fragility and increased vulnerability to mechanical agitation. It is also suspected that hyperproliferative disorders lead to increased exhaustion of metabolites used to fuel the ATP pump, leading to unstable cell membranes. Mechanical stress of blood drawing into vacutainer tubes and shaking due to pneumatic transport chutes can cause in-tube cell lysis, and thus a falsely high potassium reading.
Conclusions: Accurate potassium measurement in leukemia requires extreme care in blood sample handling, including mode of drawing, transport and processing. When there is suspicion of pseudo-hyperkalemia, using a blood gas syringe to draw blood and manually transporting it to the lab can help in accurate potassium measurement.