A term newborn develops petechiae and purpura within hours of birth. Platelet count is 25,000 per microliter; the mother's platelet count is normal. The infant's platelet antigen typing reveals incompatibility with maternal antibody specificity. The most common antigen involved in this condition is:

• A HLA-B27 antigen
• B HPA-1a (PlA1) on platelet glycoprotein IIIa ✓
• C Rhesus D antigen on red cells
• D GP Ib alpha HPA-2b antigen

Explanation

Neonatal alloimmune thrombocytopenia occurs when a mother negative for a platelet-specific antigen forms IgG antibodies against fetal platelets inherited from the father. Anti-HPA-1a, directed against glycoprotein IIIa, accounts for roughly 75 to 80 percent of clinically significant cases. Maternal platelets are normal because the antibody targets only fetal antigen-positive platelets, distinguishing it from autoimmune thrombocytopenia. Rh D is a red cell antigen relevant to hemolytic disease, not thrombocytopenia.

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.