The dog had a presumed immune-mediated intravascular and extravascular hemolytlc anemia. The bilirubin crystal (also called hematoidin) is presumed to be from phagocytized hemoglobin and conversion of the porphyrin ring of hemoglobin into bilirubin within the monocyte. Hematoidin forms under conditions of hypoxia, suggesting the dog was hypoxemic. It also possible that the monocyte obtained hemoglobin from phagocytosis of red blood cells in tissues as part of the hemolysis or underlying tissue hemorrhage and then migrated back from tissue into blood (reverse transmigration).
