Bilirubin, a yellow-brown pigment resulting from the breakdown of red blood cells, is produced when old or damaged cells release hemoglobin. This pigment undergoes processing in the liver, where it is chemically modified and excreted in bile, contributing to the yellow color of bile. Elevated bilirubin levels, indicative of various liver and blood disorders, can cause jaundice.
When excess removal of red blood cells occurs, it leads to weakness from blood loss. The liver, overwhelmed by increased bilirubin, causes jaundice with yellowing of tissues and orange or brown urine. Elevated hemoglobin in the bloodstream may damage the kidneys. Additionally, red blood cells coated with antibodies clump together, forming small clots (embolisms). These clots obstruct blood vessels, impacting organ circulation and prompting inflammation as the body tries to dissolve them.
The spleen grows larger as it processes a surplus of damaged red blood cells, overwhelming the liver with excessive bilirubin. This results in jaundice, turning the tissues yellow or orange.
Adding to the complexity, a protein system known as the complement system is triggered by these anti-red cell antibodies. This can cause the rupture of red blood cells, a process termed intravascular hemolysis. This leads to a shortage of red blood cells circulating, jeopardizing the delivery of sufficient oxygen to tissues and the removal of waste gases. This critical situation is life-threatening, with reported mortality rates ranging from 20-80%, depending on the study. For more detailed information and guidance, consult with your veterinarian.
In many cases of canine IMHA, the cause remains unknown, but investigating is crucial. To identify IMHA, your veterinarian looks for signs of red blood cell destruction, like orange urine, yellow tissues, or high bilirubin levels. Additionally, at least two indicators are needed to confirm that the destruction is immune-mediated and not caused by other factors (such as zinc toxicity). Indicators of immune-mediated destruction may include a positive auto-agglutination test, a positive Coombs test, or the presence of cells known as "spherocytes".
Coombs TestIf a dog shows signs of anemia, jaundice, or unusual blood cells on a smear, it may indicate immune-mediated hemolytic anemia. The Coomb's test helps confirm this by detecting antibodies on red blood cells. It clarifies if anemia is immune-related, ruling out other causes like bleeding or toxicity. Though not perfect, it aids in diagnosing immune-mediated issues, especially when other findings are unclear.
Serum Lactate LevelsLactate, a by-product of oxygen deprivation, indicates severe issues when elevated. High levels, especially at presentation, may predict poor outcomes. Monitoring lactate helps assess tissue oxygenation in IMHA dogs.
Testing for Blood Parasites
Blood parasites, especially from ticks, can trigger IMHA. Parasites like Ehrlichia, Babesia, and Anaplasma should be ruled out. If confirmed, targeted therapy is possible.
The patient with IMHA is often unstable, requiring quick blood transfusions if the hematocrit is dangerously low. Hematocrit is a measure of the proportion of red blood cells to the total volume of blood. It is expressed as a percentage and is an important component of a complete blood count (CBC). Supportive care addresses fluid balance and nutrition. Halting hemolysis by suppressing the immune system's red blood cell destruction is crucial, along with preventing thromboembolism.
Transfusion:Compatible blood may last 3 to 4 weeks, but IMHA poses challenges as even the patient's cells are destroyed. Cross-matching may not guarantee a good match due to the hyperactive immune response, leading to multiple transfusions.
****Immune Suppression:Corticosteroids like prednisone and dexamethasone are vital for immune suppression, targeting lymphocytes producing antibodies. Regular monitoring is crucial, and prolonged steroid use may lead to Cushing's Syndrome, with effects diminishing as the dosage decreases.
Additional Immune Suppression:If corticosteroids show minimal response, stronger agents like azathioprine or cyclosporine may be added. Mycophenolate mofetil is another emerging option. These medications aim to enhance immune suppression and reduce steroid dosage, mitigating side effects.
Treatment Duration:Expect prolonged therapy, potentially months, and don't be surprised if a second medication is added to corticosteroids. Regular monitoring and consultation with your veterinarian are essential during the treatment period. IMHA has a relapse rate of 11-15%.
The 2002 study by Drs. Anthony Carr, David Panciera, and Linda Kidd at the University of Wisconsin School of Veterinary Medicine looked for trends by reviewing 72 dogs with IMHA. Their findings are:
Prognostic Factors for Mortality and Thromboembolism in Canine Immune-Mediated Hemolytic Anemia. A.P. Carr, D. Panciera, L. Kidd. Journal of Veterinary Internal Medicine. 2002; 16: 504-509.
IMHA (Immune-mediated hemolytic anemia) is a severe and potentially life-threatening condition in dogs, marked by the immune system attacking and destroying the body's own red blood cells. Jaundice, weakness, and various complications can arise, with mortality rates ranging from 20-80%. Prompt veterinary consultation is essential, and in critical cases, transfer to a specialized facility may be necessary. Diagnosis involves thorough examination and testing, including the Coombs test and monitoring serum lactate levels. Treatment includes blood transfusions, immune suppression with corticosteroids, and additional medications if needed. Prolonged therapy and careful monitoring are crucial, as IMHA has a relapse rate of 11-15%. Understanding the signs, diagnostic procedures, and treatment options is key to managing this complex and challenging canine illness. For further details and guidance, consult with your veterinarian.
Genevieve Tan
