Question

Which of the following investigations should be done immediately to best confirm a mismatched (non-matched) blood transfusion reaction?

• A. Indirect Coombs test
• B. Direct Coombs test
• C. Antibody in the patient's serum
• D. Antibody in the donor serum

Hint:

You need the test for antibody already bound to red cells in vivo.

Answer 1

The Correct Option is B

Step 1: Understand what happens in a haemolytic transfusion reaction. The recipient's antibodies attach to the transfused (donor) red cells, coating them with antibody and complement. These coated cells are then destroyed.
Step 2: Match the test to the event. The Direct Coombs test (direct antiglobulin test, DAT) detects antibody or complement ALREADY bound to red cells in the patient's circulating blood. After a mismatched transfusion the donor cells are antibody-coated, so the DAT turns positive immediately. This is the fastest confirmatory test.
Step 3: Why not the Indirect Coombs test? The indirect test (option A) detects FREE antibodies floating in serum and is used for pre-transfusion screening and crossmatch, not for proving that an in-vivo reaction has already occurred.
Step 4: Options C and D describe serum antibody studies, which are slower and more for working out the cause later, not the immediate bedside confirmation of an acute reaction.
Step 5: So the immediate best confirmatory test is the Direct Coombs test on the recipient's post-transfusion sample.
Answer: B. Direct Coombs test.