Platelets express both platelet specific antigens such as human platelet antigens (HPAs) and antigens which are shared with other cells such as ABO and HLA class I antigens.
Currently there have been 35 HPA identified on 6 platelet membrane glycoproteins.
HPAs are polymorphisms in platelet membrane glycoproteins that can stimulate the production of alloantibodies once exposed to foreign platelets with different HPAs. HPAs can also be targeted by autoantibodies and drug-dependent antibodies.
HPA antibodies can be implicated in the following clinical conditions:
- Fetomaternal or neonatal alloimmune thrombocytopenia (FNAIT/NAIT)
- Post transfusion purpura (PTP)
- Platelet transfusion refractoriness
HPA-1a antibodies account for greater than 80% of the HPA antibodies detected and are the most common cause of both FNAIT and PTP.
HPA-matched platelets can be supplied after consultation with a Lifeblood Transfusion Medicine Specialist for the following indications:
- Thrombocytopenia due to alloimmunisation i.e. neonates with FNAIT.
- Patients who are refractory to random donor platelet transfusions due to the presence of HPA alloimmunisation.
- Patients with congenital platelet disorders including Glanzmann thrombasthenia and Bernard-Soulier syndrome.
HPA antibodies can be detected using the Platelet immunofluorescence test (PIFT) and capture assays, such as the Monoclonal Antibody Immobilisation Platelet Antigen (MAIPA).
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