Inappropriate Secondary Erythrocytosis in a Dog With Renal Sarcoma

A 7-year-old mixed breed dog was evaluated for erythrocytosis with an initial hematocrit of 82.3%. Abdominal ultrasound revealed a 6 cm mass on the cranial pole of the right kidney. Daily therapeutic phlebotomies were performed, reducing the hematocrit to 54%. The dog underwent a right nephroureterectomy, recovered without complications, and was discharged 3 days after surgery. Histopathologic evaluation revealed a completely excised grade II soft tissue sarcoma. The preoperative erythropoietin level was 7.00 mU/mL (RI 1.90-22.90 mU/mL) and the 3-day postoperative erythropoietin level was 0.99 mU/mL, supporting a diagnosis of inappropriate secondary erythrocytosis due to the renal tumor. Secondary erythrocytosis resulting from renal soft tissue sarcoma is rare. Confirmatory testing with erythropoietin levels can assist in the diagnosis of secondary erythrocytosis. Erythropoietin levels that are normal or increased in the face of erythrocytosis indicate a source of inappropriate erythropoietin production.