(515) Spurious Laboratory Values in a Critically Ill Patient: The Mystery of Leukocyte Larceny

Introduction: Severe hypokalemia can lead to fatal arrhythmias if not promptly managed. Laboratory errors can result in misleading electrolyte abnormalities which may lead to improper treatment being administered. This case highlights a patient with suspected acute myelogenous leukemia presenting with a blast crisis and persistent hypokalemia despite aggressive treatment.

Description: A 50-year-old male with untreated nasopharyngeal cancer presented with severe shortness of breath and altered mental status. Vital signs included a rectal temperature of 105.3°F, blood pressure 135/83 mmHg, heart rate 140 bpm, respiratory rate 29 bpm, and oxygen saturation 94% on ambient air. Initial arterial blood gas (ABG) analysis revealed a pH of 7.47, PaCO2 28 mmHg, PaO2 36 mmHg, HCO3 33 mmol/L, lactic acid 3.2 mmol/L, and potassium 1.6 mmol/L. No EKG changes were noted. Laboratory tests showed a white blood cell (WBC) count of 644k/μL with 100% blast-like cells. The patient was treated with leukapheresis and intubated for airway protection. A CT scan revealed a 4.2 x 2.8 cm intraparenchymal hemorrhage with mass effect and a 3 mm leftward midline shift. Despite mechanical ventilation, the patient was hypoxemic with PaO2 from 33 to 43 mmHg and ABG oxygen saturations between 71% to 87%, while continuous pulse oximetry showed saturations between 95% to 100%. Potassium levels remained low (2.1 to 3.0 mmol/L) despite aggressive repletion. When samples were placed on ice, ABGs showed normal electrolyte levels and improved oxygenation when compared with samples sent on room temperature. The family opted for comfort measures and the patient passed away the next day.

Discussion: This case demonstrates severe, refractory hypokalemia that resolved upon cooling of blood samples, suggesting pseudohypokalemia. Patients with leukemia may experience pseudohyperkalemia; however, spuriously low potassium levels are not frequently reported in literature. Spurious hypoxemia may also occur due to high leukocyte counts affecting ABG analysis. When two samples taken from the same blood draw were analyzed, the sample transported on ice showed oxygen saturation consisted with the pulse oximeter and normalized potassium levels. This highlights the importance of proper sample handling to avoid misdiagnosis and inappropriate treatment.