CE MarkEER048050

50 Tests - HPA-1 a/b

Available for QiaSymphony SP/AS - Ref: EER048032QS

HPA-1 a/b

Neonatal Alloimmune Thrombocytopenia (NAIT) is characterized by either prenatal or neonatal intracranial hemorrhage, leading to death or permanent neurological disability. It can also manifest with generalized petechiae, intra-abdominal hemorrhage, and excessive bleeding after venipuncture or circumcision.

It is caused by placental transfer of maternal platelet IgG antibodies (alloantibodies) formed against incompatible fetal platelet antigens. For example, HPA-1a (PLA-A1; Zw) negative mothers carrying an HPA-1a positive fetus develop the anti-HPA-1a antibodies that are found in 80% of neonatal alloimmune thrombocytopenia cases. Additional platelet antigens involved include HPA-5 (Br; Zv) (10% of cases), HPA-2 (Ko), HPA-3 (Bak; Lek), HPA-4 (Pen; Yuk), and HPA-6 (Ca; Tu).

Involvement of HLA class I antibodies has been suspected in a few cases, but is not yet proven. Post-transfusion purpura (post-transfusion alloimmune thrombocytopenia) is a rare disorder that occurs 5 to 10 days following transfusion of platelet-containing blood products having incompatible HLA or platelet specific antigens. Severe bleeding may occur due to antibody-induced destruction of the transfused platelets.

The platelet alloantigens are derived from single nucleotide polymorphisms in the genes coding for platelet membrane glycoproteins (eg, GPIIIa, GPIIb, etc.). For example, HPA-1a/b is associated with a 1565T>C polymorphism that leads to a substitution of proline for leucine in the GPIIIa protein. A mismatch in HPA-1 genotype between mother/fetus (mother/father) or platelet donor/recipient increases the risk of NAIT and post-transfusion reaction, respectively.