Drug-induced immune-mediated thrombocytopenia in the intensive care unit ★

• Thrombocytopenia in intensive care units is multifactorial, and an etiologic diagnosis is often challenging.
• Immune-mediated thrombocytopenia is a potential cause of severe thrombocytopenia in the intensive care units.
• Diagnosis can be challenging because many potential offenders are concurrently used.
• A definitive diagnosis should be sought to prevent future exposures to offending medications.

A 62-year-old woman with prosthetic mitral valve was admitted for explant of an infected prosthetic knee. Perioperatively, she was bridged with heparin and started on empiric vancomycin and piperacillin-tazobactam. Platelet counts dropped precipitously within 2 days reaching a nadir of 6000/μL, without any bleeding. Decline persisted despite substituting heparin with bivalirudin. Antiplatelet factor 4 and anti-PLA1 antigen were negative. Schistocytes were absent. Antibiotics were substituted with daptomycin for suspected drug-induced thrombocytopenia. Pulse dose of intravenous immunoglobulin was initiated with rapid normalization of platelet count. She tested positive for IgG antiplatelet antibodies to vancomycin and piperacillin-tazobactam thereby confirming the diagnosis. Drug-induced immune-mediated thrombocytopenia is an underrecognized cause of thrombocytopenia in the intensive care units. Clinicians should be cognizant of this entity, and a definitive diagnosis should be sought if feasible.