What is the most important diagnostic test for a delayed hemolytic transfusion reaction?

The most critical diagnostic test for a delayed hemolytic transfusion reaction is the Coombs test. This test is designed to detect antibodies that are bound to red blood cells, which are indicative of hemolysis caused by an immune response. In a delayed hemolytic reaction, the immune system may take days to weeks to produce antibodies against transfused red blood cells that are recognized as foreign.

The Coombs test, specifically the indirect Coombs test, helps to identify these antibodies in the serum, while the direct Coombs test detects antibodies attached to red blood cell surfaces. Identifying these antibodies is essential to confirm the diagnosis of a delayed hemolytic transfusion reaction and to guide appropriate clinical management, such as stopping further transfusions and monitoring the patient closely for complications.

Other tests like blood cultures, C-reactive protein, and complete blood count, while useful in different clinical contexts, do not specifically address the immunologic response associated with a delayed hemolytic reaction. Blood cultures are used to identify infections, C-reactive protein is a marker of inflammation that might suggest infection or inflammation, and a complete blood count provides overall information on blood components but does not pinpoint the cause of hemolysis. Thus, the Coombs test stands out