Neonatal alloimmune thrombocytopenia due to anti-HPA-1b and anti-HLA antibodies: diagnostic and transfusion management of a clinical case

Abstract

Fetal and Neonatal Alloimmune Thrombocytopenia (FNAIT) is a rare condition affecting approximately 1 in 1,500 pregnancies. It is caused by maternal alloantibodies directed against paternal human platelet antigens (HPA) inherited by the fetus, which can result in FNAIT and an increased risk of bleeding. In Caucasians around 80% of the FNAIT cases are caused by HPA-1a alloantibodies while anti-HPA-5b are responsible for 10-15 % of the cases. 

We present the case of a full-term female neonate, born by spontaneous vaginal delivery without infectious complications or signs of fetal distress. Within the first 24h of life, a severe thrombocytopenia was discovered on neonate blood cell count (PLT=8×10⁹/L), so an alloimmune syndrome was suspected due to the severity and early onset of thrombocytopenia. The newborn underwent platelet transfusion therapy and FNAIT investigations on parental and newborn samples were performed.

Maternal screening tests for anti-HPA antibodies, using two different technologies, and HLA antibody identification assay, pointed out anti-HPA-1b antibodies together with class I anti-HLA antibodies in maternal serum. HPA genotyping confirmed incompatibility for HPA-1 antigen while HLA typing revealed the presence of a mismatch allele between mother and neonate. The diagnosis of FNAIT was proved and transfusion therapy was driven to HPA-HLA platelet selected units.

This case highlights the importance of referral to a reference laboratory equipped with diverse diagnostic tools and an efficient blood bank. Such resources are essential for accurate diagnosis and optimized treatment, particularly when rare HPA and/or HLA alloantibodies are involved.