Evaluation of the Patient with Hemolysis

The clinical picture of the dog or cat with HA is nonspecific and may relate not only to hemolysis, but also to an underlying disease process. Although anemia due to defective or deficient RBC production is often insidious in onset, HA frequently results in an acute illness. As a result of the anemia and decrease in oxygen delivery to the tissues, owners may notice exercise intolerance, anorexia, general malaise, syncope or collapse, or pallor. On physical examination, pale mucus membranes are a characteristic finding and icterus is often noted. Other findings may include tachycardia, tachypnea, bounding pulse, and a soft systolic basilar heart murmur.

Hemolysis, which occurs predominantly extravascularly, may also occur inside the vascular space. Either way, breakdown of RBCs leads to release of bilirubin; bilirubinemia and bilirubinuria are consistent with either intravascular or extravascular pathologic hemolysis.¹ Hemoglobinemia and hemoglobinuria are found only with intravascular hemolysis. Several disease states cause both intravascular and extravascular hemolysis. When intravascular hemolysis predominates, the disease process often carries a poorer prognosis for recovery than diseases associated with predominantly extravascular hemolysis.¹

Hemolysis is associated with numerous changes in RBC appearance, and these changes are often a key to identifying the cause.¹ There is no substitute for a thorough evaluation of a well-stained blood smear using oil immersion and high magnification; blood cell counts alone are inadequate for the evaluation of an animal with suspected hemolysis. Shape changes may point to a specific cause. For example, schistocytes suggest fragmentation, spherocytes suggest immune-mediated destruction (Color Plate 121-1), and Heinz bodies suggest oxidative damage (Color Plate 88-2). Additionally, erythrocytic parasites may be observed microscopically.

Regardless of the cause of hemolysis, certain therapeutic principles apply. Heme pigments released by hemolysis can cause nephrotoxicity in humans. Although acute renal failure resulting from hemolysis is not reported in small animals, adequate renal perfusion should be maintained to minimize this risk. Supportive care for animals with severe or rapid-onset anemia includes provision of either transfused RBCs or purified hemoglobin solution. The need for transfusion should be based on not merely an RBC count, hemoglobin measurement, or PCV but on clinical assessment (e.g., mental state, activity level, heart and respiratory rates, pulse quality). A packed RBC transfusion provides oxygen carrying capacity with less volume than whole blood and is often preferred in animals with hemolysis (see Chapter 66, Transfusion Medicine). Transfusion in cats must follow blood typing of both donor and recipient; blood typing of recipient dogs is not required for first-time transfusions or if only DEA 1.1-negative blood is transfused. Although transfusion of cross-matched blood is ideal, first transfusions in dogs and transfusion of blood-type compatible cats are usually successful without cross-matching.² Transfused RBCs may be susceptible to the same cause of hemolysis as native RBCs. Purified hemoglobin (Oxyglobin) solutions do not require cross-matching or blood typing, although the future availability of these products is unknown.