A 77-year-old gentleman with a history of hypertension developed worsening weakness of a month duration. His blood work at an outside facility revealed severe leukocytosis. He was transferred to University of Arizona Medical Center for leukapheresis. His initial lab data revealed WBC count of 347.2X1000/microL (Normal 3.4-10.4X1000/microL) with 90% blasts. His pulse oximetry was 92% on 4 L/min oxygen, although his arterial blood gas showed a pO2 of 46 (Normal 70-95 mm Hg) due to hyperleukocytosis and enhanced metabolic activity of malignant cells. His electrolyte panel showed pseudohypokalemia with potassium level of 2.4 (Normal 3.5-5.1 mMol/L).