Warm autoimmune hemolytic anemia is the most common form of autoimmune hemolytic anemia (see this term) defined by the presence of warm autoantibodies against red blood cells (autoantibodies that are active at temperatures between 37-40°C).
Warm auto-antibodies are responsible for 60/70% of AIHA, whose annual incidence is estimated to be between 1/35,000-1/80,000 in North America and Western Europe.
Warm AIHA is more common in women (female to male ratio approximately 2:1 in adults). The disease is characterized by symptoms due to the anemia including fatigue, exertional dyspnea, and, more rarely, jaundice and dark urine in case of severe hemolysis. If the disease is severe, fever, chest pain, syncope or heart failure may occur. Hemolysis occurs mainly in the spleen, so mild splenomegaly is relatively common.
Approximately half of cases of warm AIHA are primary (idiopathic) while the other half are secondary to an underlying condition, frequently chronic lymphocytic leukemia or an autoimmune systemic disease such as systemic lupus erythematosus (SLE; see this term).
Diagnosis is based on clinical and laboratory evidence of hemolytic anemia and the detection of autoantibodies with the direct anti-globulin test (DAT). Typically in warm AIHA, the DAT pattern is IgG alone or IgG with complement C3.
The differential diagnosis of warm AIHA includes a post-transfusional alloimmune hemolytic anemia and, when the DAT is negative (less than 5% of all warm AIHAs), every other cause of either hereditary or acquired hemolytic anemia.
The most common therapy and the cornerstone of treatment for warm AIHA are corticosteroids. If these are ineffective, splenectomy can be considered. Rituximab has become an option in refractory disease and the use of immunosuppressors can be helpful in chronic severe refractory cases.
Warm AIHA is often severe but death is usually a rare outcome, except in elderly patients who have a higher risk of cardiovascular manifestations (in cases with severe anemia) and also of severe treatment-induced infections. Prognosis depends on the underlying condition.
- Pr Marc MICHEL