A neonate develops severe hemolytic anemia. Peripheral smear shows nucleated RBCs and polychromasia. The direct Coombs (DAT) test is strongly positive. The most likely mechanism is:

• A G6PD deficiency triggered by oxidant exposure
• B Hereditary spherocytosis with membrane protein defect
• C Maternal IgG antibodies crossing the placenta and coating fetal RBCs ✓
• D Pyruvate kinase deficiency with intracorpuscular enzyme defect

Explanation

Hemolytic disease of the newborn is caused by maternal IgG (which crosses the placenta) directed against fetal RBC antigens (most commonly Rh D). The IgG coating the fetal red cells is detected by the direct antiglobulin (Coombs) test. G6PD, hereditary spherocytosis, and pyruvate kinase deficiency are intrinsic/intracorpuscular defects and give a negative DAT.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.