The direct Coombs test differs from the indirect Coombs test in that it detects:
- A Free circulating antibody in maternal serum
- B Antibody bound to red cells in vivo, requiring only the addition of antihuman globulin ✓
- C Complement components in the patient's serum
- D Antigen-antibody complexes after incubation of patient serum with test red cells
Correct answer: B. Antibody bound to red cells in vivo, requiring only the addition of antihuman globulin
Explanation
The direct antiglobulin (Coombs) test detects antibody or complement already attached to red cell surfaces in vivo, as in haemolytic disease of the newborn, autoimmune haemolysis and transfusion reactions. Only antihuman globulin is added, causing visible agglutination if cells are coated. The indirect test incubates patient serum with known red cells to detect free circulating antibody, which is what option A describes; that two-step design belongs to the indirect method and is therefore the distractor to reject.
Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.