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Profound piperacillin‐mediated drug‐induced immune hemolysis in a patient with cystic fibrosis

A 23-year-old woman with a history of cystic fibrosis presented to our hospital with acute respiratory failure. She was admitted to the medical intensive care unit and started on intravenous piperacillin-tazobactam for treatment of presumed Pseudomonas aeruginosa pneumonia. At admission, the patient’s hemoglobin (Hb) level was 13.1 g/dL (normal range, 11.8-16 g/dL). During the first 11 days of her hospitalization, her Hb level ranged from 8.4 to 9.8 g/dL. On Hospital Day 12, her Hb began to trend down, reaching a nadir of 4.7 g/dL on Hospital Day 15 despite transfusing 2 units of red blood cells (RBCs; see figure, left, trend of hemolysis-related labs during hospitalization). The reticulocyte count was 10.4% on Hospital Day 14. Initially, the etiology of this anemia was unknown; however, examination of the peripheral blood smear demonstrated marked anemia, polychromasia, and profound microspherocytosis (approx. 65% of total RBCs, see figure, middle,Wright’s stain of the patient’s peripheral blood smear on Hospital Day 15, 1000¥ magnification), which prompted further workup. Her lactate dehydrogenase was elevated to 531 U/L (normal range, <226 U/L) and total bilirubin was increased at 2.9 mg/dL (normal range, 0.2-1.2 mg/dL). Her serum haptoglobin was 122 mg/mL (normal range, 16-200 mg/mL) before the transfusion of RBCs, but decreased to 0 mg/mL afterward. The direct antiglobulin test was 3+ positive for immunoglobulin G and negative for complement. The eluate was negative. Due to suspicion for drug-induced immune hemolytic