Hyperkalemia Versus Pseudohyperkalemia Without ECG Changes in Acute Blast Crisis Progressing to Tumor Lysis Syndrome.

Hyperkalemia is critical to recognize, but distinguishing it from pseudohyperkalemia is essential to avoid unnecessary treatment. We present a 66-year-old male with a history of myeloproliferative disorder and chronic myelomonocytic leukemia (CMML) who developed hyperleukocytosis (white blood cell (WBC) 666 × 10⁹/L, 95% blasts) and severe hyperkalemia (9.4 mmol/L) without electrocardiogram (ECG) changes. Pseudohyperkalemia was considered but ruled out by measuring serum and plasma potassium levels along with using heparinized and non-heparinized tubes. Pseudohyperkalemia is more common in hematologic malignancies due to extreme leukocytosis, which leads to an increase in cell fragility and potassium leakage during sample handling. Despite initial medical therapy, hyperkalemia persisted, requiring emergent hemodialysis, leukapheresis, and cytoreductive treatment. He developed tumor lysis syndrome (TLS), necessitating rasburicase and continuous renal replacement therapy. This case underscores the challenges of hyperkalemia in hematologic malignancies and the importance of rapid differentiation from pseudohyperkalemia.