imha

Immune-mediated hemolytic anemia (IMHA) is an autoimmune disorder in which antibodies target red blood cells, causing their destruction and hemolytic anemia. It can be idiopathic (primary) or secondary to infections, drugs, neoplasia, or vaccines.

In warm IMHA, typically IgG antibodies coat red blood cells leading to extravascular hemolysis mainly in the spleen; cold agglutinin disease involves IgM antibodies and complement, which can cause intravascular hemolysis. The direct antiglobulin test (Coombs test) detects bound antibodies or complement on red cells and helps support the diagnosis. Warm IMHA is the more common form in dogs.

IMHA is most commonly diagnosed in middle-aged dogs; cats and humans can be affected but less frequently. Primary IMHA has no identifiable trigger, whereas secondary IMHA is associated with infections, cancer, drugs, or immune dysregulation. Clinical signs reflect anemia and may include pale mucous membranes, weakness, tachycardia, jaundice, dark urine, and sometimes splenomegaly; red blood cell agglutination may be observed on a smear.

Diagnosis relies on complete blood count showing anemia with reticulocytosis, peripheral smear findings such as spherocytes and sometimes agglutination, elevated bilirubin, and decreased haptoglobin. A positive Coombs test supports immune-mediated destruction, while guidelines call for exclusion of other causes of hemolysis and evaluation for underlying triggers.

Treatment focuses on stabilization and immunosuppression. Corticosteroids are typically first-line, with second-line immunosuppressants such as azathioprine, mycophenolate, or cyclosporine used as needed. Management may require red blood cell transfusions and supportive care; addressing any underlying cause is important.

Prognosis is variable. Many patients respond to therapy, but relapses are common and long-term management is often required. Outcome depends on severity, response to treatment, and presence of any underlying trigger.