INTRODUCTION
Platelets are active cells, which assist in hemostasis and blood coagulation. Their glycocalyx contains glycoproteins (GP) molecules through which platelet bind to other cells to perform their functions. The GPs (GPIa, GPIb, GPIIb and GPIIIa,) are produced by substitutions of single amino acid. Human platelet antigens (HPAs) are polymorphic amino acid sequences found on these GPs
GPIIIa is considered the most polymorphic glycoprotein and bears HPA-1, HPA-4, and HPA-6. HPA-1 is defined as the most important antigenic system. HPA-1a or HPA-1b antigens are due to the existence of leucine or proline at position 33 of the GPIIIa where the “a" represents the common allele and the “b" represents the rare allele.
HPA are associated with alloimmunization as they are the targets for platelet antibodies that lead to platelet destruction in post-transfusion refractoriness (PTR) and purpura (PTP) after platelet transfusion. Patients who are treated for hematological diseases associated with thrombocytopenia are highly vulnerable to platelet refractoriness when treated by prophylactic concentrated platelet transfusions to prevent bleeding. Consequently, accurate donor compatibility for platelet transfusions is very essential.