A neonate born to an Rh-negative mother who did not receive prophylaxis develops jaundice within 24 hours. Cord blood testing shows that incubation of the infant's red cells with antihuman globulin produces visible agglutination. Which test has been performed and what does the positive result indicate?
- A Direct Coombs test, maternal antibody bound to the infant's red cells in vivo ✓
- B Indirect Coombs test, maternal antibody circulating freely in infant serum
- C Direct Coombs test, antibody present only in the mother's serum
- D Indirect Coombs test, antibody bound to the infant's red cells
Correct answer: A. Direct Coombs test, maternal antibody bound to the infant's red cells in vivo
Explanation
The direct Coombs (antiglobulin) test adds antihuman globulin directly to the patient's washed red cells and detects antibody or complement already bound in vivo, here maternal anti-Rh coating fetal erythrocytes in haemolytic disease of the newborn. The indirect Coombs test instead looks for free antibody in serum by incubating it with known red cells first, so options describing the indirect format are incorrect.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.