Final answer:
The most important test for immune hemolytic anemia is the direct Coombs' test, which checks if the patient's red blood cells are bound by immunoglobulin or complement. It is performed by adding Coombs' reagent to the blood sample and observing for agglutination.
Step-by-step explanation:
The most important test for immune hemolytic anemia is the direct Coombs' test, also known as the direct antiglobulin test (DAT). This test is used to determine if the patient's red blood cells are already bound by immunoglobulin (or complement). It is performed by adding Coombs' reagent, which contains antihuman IgG antibodies, to the patient's blood sample. If agglutination occurs, it indicates the presence of bound immunoglobulin or complement on the red blood cells, confirming immune hemolytic anemia.