A term newborn develops jaundice within 24 hours of birth. Mother is Rh negative and unimmunised; baby is Rh positive. The peripheral smear shows spherocytes and the reticulocyte count is raised. The single best test to demonstrate antibody coating the baby's red cells is:

• A Indirect antiglobulin (Coombs) test on maternal serum
• B Rose-Waaler test on neonatal serum
• C Direct antiglobulin (Coombs) test on cord red cells ✓
• D Cold agglutinin titration on neonatal serum

Explanation

The direct Coombs test detects antibodies or complement components already bound to red cells in vivo, so it is the definitive test in haemolytic disease of the newborn and autoimmune haemolysis. The indirect Coombs detects free antibody in serum, such as screening a pregnant Rh negative mother, but does not show coating of the infant's cells. Spherocytosis with reticulocytosis supports immune haemolysis rather than hereditary spherocytosis 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.