A 4-year-old, female spayed, Rottweiler weighing 53.3 kg presented to the William R. Pritchard Veterinary Medical Teaching Hospital (VMTH) at the University of California, Davis for the primary complaint of epistaxis of 3 days' duration. Initial physical examination revealed severe bilateral epistaxis as well as petechiation and ecchymoses along the ventrum, inner pinnae, conjunctiva, and buccal mucosa. Melena was noted on rectal examination. A CBC revealed severe thrombocytopenia (14,000/mL; reference range, 150,000-400,000/mL); mild normocytic, normochromic nonregenerative anemia (PCV, 36%; reference range, 40-55%); and a normal leukogram (9,600 WBC/mL; reference range, 6,000-13,000 WBC/mL). Serum biochemistry results included mildly increased BUN concentration (23 mg/dL; reference range, 5-21 mg/dL), increased activities of alkaline phosphatase (ALP) (835 IU/L; reference range, 21-170 IU/L) and GGT (7 IU/L; reference range, 0-6 IU/L), and mild hypercholesterolemia (406 mg/dL; reference range, 135-361 mg/dL). Urinalysis (obtained by voiding) revealed a specific gravity of 1.030 with proteinuria (30 mg/dL). A bone marrow aspirate revealed mild megakaryocytic hyperplasia consistent with immune-mediated thrombocytopenia (IMTP). Thoracic radiographs and an abdominal ultrasound were normal. Serologic titers for Ehrlichia canis, Anaplasma phagocytophilum, Rickettsia rickettsii, and Babesia canis were negative.Treatment with prednisone (1 mg/kg PO q12h) and azathioprine (1.4 mg/kg PO q24h) was initiated. The platelet count remained below 14,000/mL for 8 consecutive days and epistaxis, petechiation, and melena persisted. Because of progressive anemia (PCV, 20%) as well as clinical signs of weakness and tachycardia, a cross-matched packed red blood cell (pRBC) transfusion was administered. The dog received 300 mL of pRBCs at an initial rate of 2 mL/kg/h, which then was increased to 4 mL/kg/h. The posttransfusion PCV was 28%. Two hours after the transfusion, the dog's rectal temperature increased from 101 to 1041F. A transfusion reaction was suspected and the dog was treated with dexamethasone (0.15 mg/kg IV, once) and diphenhydramine (2.0 mg/kg SC, once). Rectal temperature decreased to 101.51F over the next 4 hours and no other adverse effects were noted. Cyclosporine (3.8 mg/kg PO q12h) was added to the treatment regimen on day 8, and the dose of azathioprine was decreased (1.4 mg/kg PO q48h). On day 10, the platelet count increased to 48,000/mL and the dog was discharged from the hospital. Treatment at discharge included prednisone (1 mg/kg PO q12h), azathioprine (1.4 mg/kg PO q48h), cyclosporine (3.8 mg/kg PO q12h), and famotidine (0.5 mg/kg PO q12h).The dog was reevaluated on day 12 after initial presentation. Physical examination was unremarkable with resolution of petechiation and melena. A CBC revealed regenerative anemia (PCV, 22.8%; reticulocyte count, 210,900/mL; reference range 7,000-65,000/mL), mature neutrophilia (12,737/mL; reference range, 3,000-10,500 cells/mL), and a platelet count of 79,000/mL. A tro...