Human platelet antigen 1a (HPA-1a) is the most common HPA implicated in fetal and neonatal alloimmune thrombocytopenia (FNAIT) cases.
In pregnancies affected by FNAIT, maternal HPA-1a antibodies cross the placenta, bind to the baby’s blood platelets and progressively destroy them. If you have HPA-1a antibodies, blood and platelet donation is not recommended due to the potential associated risks for donation recipients.
What is FNAIT?
Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a rare but serious condition that affects 0.1% of pregnancies in which a pregnant mother’s immune system produces antibodies against the platelets of her fetus. This occurs when a fetus inherits platelet antigens from the father that are not compatible with the mother, typically involving a protein called human platelet antigen (HPA). The mother’s immune system recognizes the fetal platelets as foreign, attacking and destroying them, leading to low platelet levels (thrombocytopenia) in the fetus or newborn.
What are HPA-1a antibodies?
In a FNAIT-affected pregnancy, an HPA-1a negative mother develops antibodies against her HPA-1a-positive baby. The fetal platelet antigens are inherited from the father, and the mother’s immune system mistakenly identifies them as foreign and attacks them, as part of an immune response. When the baby’s platelets are destroyed, this causes thrombocytopenia or a low platelet count, causing the baby’s blood to lose the ability to clot. This leads to bleeding and hemorrhage, with life-threatening consequences if undiagnosed and left untreated.
How do you know if you have HPA-1a antibodies?
A blood test will determine whether or not you have HPA-1a antibodies. If you’ve already had a confirmed FNAIT pregnancy, you will still carry the HPA-1a antibodies in your blood. It is also possible to have unknowingly received the HPA-1a antibodies via a platelet transfusion.
Learn more about FNAIT signs and symptoms
How do HPA-1a antibodies affect blood and platelet donations?
Guidelines for donating blood can vary from state to state, so you will need to consult your local blood center to determine whether or not you are eligible to donate blood. In most cases, if you have HPA-1a antibodies, you will likely be discouraged from donating platelets and blood.
What are the potential risks of HPA-1a blood transfusions?
Blood centers often conduct screening for antibodies and HPA-matched platelets are supplied to the transfusion recipients with FNAIT to avoid risks of complications. HPA-1a negative blood transfusions can have potentially harmful outcomes in the following cases:
- In pregnant women who already have HPA-1a antibodies, a transfusion of blood containing HPA-1a antibodies could increase their antibody levels, leading to a greater risk of severe FNAIT for future pregnancies.
- In newborns with FNAIT, receiving an additional dose of HPA-1a antibodies could worsen their thrombocytopenia and lead to a life-threatening brain hemorrhage or other internal bleeding.
- If an HPA-1a-positive recipient receives a transfusion containing HPA-1a antibodies, their platelets could be destroyed, and lead to severe thrombocytopenia. This is called post-transfusion purpura (PTP) and can be a sudden and severe reaction.
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