The direct Coombs test is used primarily to diagnose which condition?

The direct Coombs test is primarily used to diagnose autoimmune hemolytic anemia. This test detects antibodies that are bound to the surface of red blood cells, indicating that the body is mistakenly attacking its own red blood cells, which is characteristic of autoimmune hemolytic anemia. When a patient has this condition, the direct Coombs test will show a positive result due to the presence of these autoantibodies.

While the direct Coombs test can also be relevant in other conditions, such as hemolytic disease of the newborn, its primary role and most significant application is in diagnosing autoimmune hemolytic anemia. This condition can encompass various forms, including warm antibody hemolytic anemia and cold agglutinin disease, all of which involve the immune system erroneously attacking the body's own red blood cells.

In contrast, conditions like iron deficiency anemia and physiologic anemia do not typically involve immune-mediated destruction of red blood cells, thus they would not result in a positive direct Coombs test.