IMHA: Diagnosing and treating a complex disease - Veterinary Medicine
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IMHA: Diagnosing and treating a complex disease
Differentiating IMHA from other causes of hemolytic anemia is challenging, but a careful diagnostic process will help you determine whether your veterinary patients will require long-term immunosuppressive therapy.



Rules of thumb for diagnosing and treating IMHA in dogs and cats
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 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 specific history. Ask questions regarding a wide range of environmental and historical circumstances to determine the following:

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 fights

6. Recent tick exposure or bee stings

7. Heartworm preventive status

8. Reproductive status

9. Signs related to other underlying disease, such as hematemesis (zinc-containing foreign body), vaginal discharge (pyometra), or weight loss and malaise (neoplasia).


Baseline tests recommended for diagnosing IMHA and investigating causes of secondary IMHA include a complete blood count, a reticulocyte count, a serum chemistry profile, 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 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/l) can 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 profile abnormalities may reflect 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, inflammation, 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 reflect 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.


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