A newborn develops jaundice within 24 hours of birth. The mother is Rh negative and was not given anti-D prophylaxis. The baby's peripheral smear shows numerous nucleated red cells and spherocytes. Which test performed on the baby's cord blood will directly demonstrate antibody-coated infant red cells?
- A Indirect Coombs test on the cord blood cells
- B Direct Coombs test using anti-human globulin added to washed cord blood cells ✓
- C Rose-Waaler test on maternal serum
- D Cold agglutination test at 4 degrees Celsius
Correct answer: B. Direct Coombs test using anti-human globulin added to washed cord blood cells
Explanation
In haemolytic disease of the newborn, maternal IgG anti-D coats the infant's erythrocytes in vivo. The direct antiglobulin (Coombs) test adds anti-human globulin to the washed baby's red cells, causing visible agglutination if they are already coated. The indirect Coombs test detects free antibodies in serum and is used to screen the mother, not the baby. The cold agglutination test detects IgM antibodies of mycoplasma infection and is irrelevant here.
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.