S6151 Reactive Pancytopenia in the Setting of Partial Small Bowel Obstruction: A Rare Hematologic Manifestation

Introduction: Neutropenia and pancytopenia typically result from infection, malignancy, autoimmune processes, or drug-related causes. We present a rare case of reversible pancytopenia triggered by intra-abdominal stress from a partial small bowel obstruction (SBO) without identifiable infectious or malignant etiology. Case Description/Methods: A 78-year-old man with a history of early-stage colon cancer (status post ileostomy and reversal), atrial fibrillation/flutter post-cardioversion, hypertension, hyperlipidemia, hernia repair, and prior partial lobectomy in infancy presented with abdominal pain. He was admitted for recurrent SBO, presumed secondary to adhesions. Imaging showed mesenteric edema, postsurgical changes, and dilated small bowel loops with air; contrast reached the colon, consistent with partial SBO. The patient was managed conservatively with bowel rest, nasogastric decompression, and ambulation. Within 24 hours, labs revealed new-onset pancytopenia: WBC fell from 10.0 to 1.4 × 10³/μL, ANC from 8.1 to 0.7, and platelets from 177 to 133. He had no prior cytopenias, chemotherapy exposure, or active infection. Workup including viral panels, blood cultures, GI panel, and C. difficile testing was negative. Macrocytosis developed (MCV rose from 93.4 to 98.1 fL), but B12 and folate levels were normal. Hemoglobin and hematocrit remained stable. By discharge, labs improved (WBC 3.7, ANC 2.5, Plt 171, MCV 97.5). Hematology attributed the cytopenias to reactive marrow suppression from intra-abdominal stress. His SBO resolved with conservative management, and counts normalized over 72 hours. Discussion: This case illustrates a rare hematologic response to partial SBO. While inflammation usually induces leukocytosis, this patient developed profound neutropenia and pancytopenia without infection, malignancy, or drug-induced suppression. The likely mechanism was transient bone marrow suppression from intra-abdominal inflammatory stress and cytokine release. Recognizing this self-limited, non-infectious phenomenon can help avoid unnecessary antibiotics, invasive workup, and delays in care. Given the recurrent nature of adhesive SBO, clinicians should monitor for this reactive marrow suppression and manage supportively.