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.



A steady or rising hematocrit, increasing reticulocytes, and decreasing spherocytes indicate a positive response to therapy.1 Medication tapering usually does not begin until the hematocrit is normal. Tailor drug tapering to the individual patient. Glucocorticoids can be tapered by about 25% every three to four weeks. If an underlying disease has been addressed or the response to treatment is rapid, drug tapering can occur more quickly. Measure the hematocrit five to seven days after discharge and again after each decrease in drug dosage. Perform a complete blood count, reticulocyte count, blood smear, serum chemistry profile, urinalysis, and urine culture every four to eight weeks as needed to monitor for drug side effects, infections, and disease relapse.

A recent study documented that about three months of therapy was sufficient in dogs successfully treated for IMHA, although a subset of dogs needed longer treatment.3 A written drug-tapering and recheck schedule can be provided for the owners to follow, under the supervision of a veterinarian. After finishing all medications, rechecks should occur quarterly for a year, then biannually.

Relapse of disease has been documented to be roughly 12% to 24%, although different protocols and studies make comparison difficult.3,13 If relapse occurs, reinstitute medications at high dosages and taper more slowly. The mortality associated with IMHA is documented to be between 29% and 70%, with a large percentage of deaths occurring within the first two weeks of diagnosis.3 Predictors of increased mortality in dogs include increased blood urea nitrogen concentrations, decreased platelets, and petechiae at the time of diagnosis. Dogs that survive the first two weeks after diagnosis have a six-month survival rate of 92.5%.3


In cats, IMHA is most often secondary to feline leukemia virus (FeLV) or Mycoplasma haemofelis (formerly Haemobartonella felis) infection although it can also be seen with other infections (feline infectious peritonitis, Cytauxzoon felis infection), drug therapy (methimazole, propylthiouracil), toxins (onions), and neoplasia (lymphoma).40,41 One study documented no increased risk of IMHA in hospitalized cats given subcutaneous vs. intravenous famotidine.42

If you suspect IMHA in a cat based on history, clinical signs, and routine diagnostic test results, perform a FeLV test. Patients with FeLV infection often respond well initially to treatment but eventually succumb to the disease. Cats with M. haemofelis infection typically have recurrent episodes of hemolytic anemia. These organisms can sometimes be seen on a blood smear, although the best test is a PCR. Treat cats with antibiotics, immunosuppressive therapy, and blood transfusions as needed.1

Similar to dogs, cats with IMHA are initially started on immunosuppressive dosages of glucocorticoids. Little information is available describing the addition of secondary or tertiary immunosuppressive medications in cats with severe IMHA. Possible drugs to add include cyclosporine or cyclophosphamide.41


When IMHA is first identified, inform owners that the prognosis is variable, treatment is labor-intensive, hospitalization is expensive, and side effects from medications can be severe. Further, since RBC counts and overall stability are often erratic in these patients, prepare owners for the roller-coaster nature of this disease. Owners also need to be prepared for frequent and costly recheck examinations.

Although IMHA is a serious condition, patients can have a good prognosis if they respond to treatment, tolerate the side effects of medications needed for treatment, and do not succumb to secondary infections or thromboembolism. The identification and treatment of underlying disease, the advent of new immunosuppressive drugs, and good supportive and owner care all contribute to increased survival in patients with IMHA.


Special thanks to Jennifer Neel, DVM, DACVP, assistant professor of clinical pathology, Department of Population Health and Pathobiology, College of Veterinary Medicine, North Carolina State University, for providing the photographs in this article.

Nicole Shaw, DVM, DACVIM
Veterinary Emergency and Referral Group
318 Warren St.
Brooklyn, NY 11201

Karyn Harrell, DVM, DACVIM
Department of Clinical Sciences
College of Veterinary Medicine
North Carolina State University
Raleigh, NC 27606


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