Veterinary Medicine - December 2008 - (Page 664)

Immune-mediated hemolytic anemia PEER-REVIEWED is initiated when the surface becomes coated with complement and either IgM or IgG.8 The most common form of IMHA is IgG-mediated. The IgG-coated RBCs are destroyed by macrophages located in the liver or spleen (extravascular). Macrophages either consume the entire erythrocyte or remove a portion of the membrane, leaving smaller RBCs with no central pallor (spherocytes). These rigid spherocytes are then trapped in the spleen and destroyed. IgM-coated RBCs will also activate complement more ef ciently than IgG, with destruction generally occurring within vessels (intravascular).1 1. Propensity to ingest foreign objects 2. Diet and treat history (e.g. recent ingestion of onions or garlic) 3. Recent history of vaccine or drug administration 4. Travel history 5. History of transfusions or recent dog ghts 6. Recent tick exposure or bee stings 7. Heartworm preventive status 8. Reproductive status 9. Signs related to other underlying disease, such as hematemesis (zinccontaining foreign body), vaginal discharge (pyometra), or weight loss and malaise (neoplasia). have clinical signs such as petechiation, ecchymosis, epistaxis, or melena. Low platelet counts have been associated with a greater risk of thromboembolism and a higher mortality rate in dogs.12 Serum chemistry proﬁle Serum chemistry pro le abnormalities may re ect organ damage from hypoxia while also indicating an underlying disease process. Elevated liver enzyme activities (alkaline phosphatase, alanine transaminase, and aspartate transaminase) and serum bilirubin concentrations are common.13 Even before glucocorticoid administration, many patients can have elevated liver enzyme activities from hepatic hypoxia, in ammation, or necrosis.13 Bilirubin concentrations can also be normal if the hemolysis has been chronic and the liver has had time to metabolize the bilirubin.1 Some studies have found a correlation between elevated bilirubin concentrations and increased mortality, while others have not.12-14 Other serum chemistry abnormalities may re ect underlying conditions. A recent study concluded that an increased blood urea nitrogen concentration and band neutrophils, a decrease in platelets, and petechiation at the time of diagnosis were all negative prognostic indicators in dogs presenting with primary IMHA.3 Anecdotally, the presence of intravascular hemolysis also appears to impart a poorer prognosis in these patients. SIGNALMENT, HISTORY, AND CLINICAL SIGNS IN DOGS The age of onset of IMHA in a patient varies; however, the disease frequently occurs in young to middle-aged dogs. Females may be predisposed to developing IMHA. Patients can have an acute or a chronic history of malaise. Vomiting or diarrhea may occur before the classic signs of anemia, which are lethargy, inappetence, polyuria, polydipsia, pallor, tachypnea, and changes in urine color. Clinical signs can include weakness, pale or DIAGNOSTIC TESTS IN DOGS Baseline tests recommended for diagnosing IMHA and investigating causes of secondary IMHA include a complete blood count, a reticulocyte count, a serum chemistry pro le, a blood smear, a slide agglutination test, a direct Coombs test, and abdominal and thoracic radiography. Complete blood count Complete blood count abnormalities usually include a regenerative anemia, although as many as 33% to 50% of dogs with IMHA can have nonregenerative As many as 33% to 50% of dogs with IMHA have a nonregenerative anemia. icteric mucous membranes, bounding pulses, tachypnea, tachycardia, hepatosplenomegaly, or a heart murmur. A patient’s clinical signs may be related to an underlying disease process rather than the anemia itself.1 To investigate potential underlying causes of IMHA, obtain a thorough and speci c history. Ask questions regarding a wide range of environmental and historical circumstances to determine the following: anemia because of an immune attack at the level of the bone marrow or early disease.9,10 A mild to marked increase in the white blood cell count can be seen, occasionally with a left shift and toxic neutrophils. This leukocytosis can be a result of many factors, including glucocorticoid-induced leukocytosis, anemic hypoxia, thromboembolic disease, and tissue necrosis.11 A patient presenting with concurrent severe thrombocytopenia (< 50,000 platelets/µl) can Macroagglutination and blood smear evaluations Preparing two blood slides is imperative in diagnosing IMHA and should be performed at the outset in every suspected case. On the rst slide, mix a drop of blood with a drop of saline solution, gently agitate the mixture, and then visually inspect it for macroagglutination. On the second slide, you can evaluate a blood smear in-house and also send it to a clinical pathologist for evaluation of spherocytes (Figure 1), Heinz bodies, blood parasites, and microagglutination (Figure 2). Spherocytes and erythrocyte macroagglutination and microagglutination are commonly found 664 December 2008 VETERINARY MEDICINE

Table of Contents Feed for the Digital Edition of Veterinary Medicine - December 2008

Veterinary Medicine - December 2008 Contents Letters Thanking Our Valued Reviewers Practical Matters Idea Exchange Why Do Dogs and Cats Eat Grass? Managing Atypical and Critical Cases of Primary Hypoadrenocorticism in Dogs Behaviors Suggestive of Postoperative Pain in Cats What to Consider When Considering Digital Radiography Avoid Common Bandaging Mistakes in Dogs and Cats IMHA: Diagnosing and Treating a Complex Disease CE Form/Advertiser Index Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - December 2008

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