Doctors use platelet immunology tests use to diagnose conditions in which the immune system mistakenly targets, attacks or destroys platelets.
This includes fetal and neonatal alloimmune thrombocytopenia (FNAIT), which occurs when maternal antibodies target the human platelet antigens (HPAs) the fetus inherited from the father that the mother does not have. Since her immune system does not recognize it as her own, the infant’s DNA may be seen as foreign, and the mother’s body will begin to produce antibodies against it.
FNAIT may be suspected when a fetus or infant has unexplained thrombocytopeniaThrombocytopenia A platelet count that is lower than normal. (low platelet counts), bleeding or intracranial hemorrhageBrain bleed Bleeding inside the fetal brain, also known as an intracranial hemorrhage. In FNAIT, it's often caused by severe thrombocytopenia and can lead to long-term disability or death. . A history of FNAITFetal and neonatal alloimmune thrombocytopenia A rare condition in which a mother’s immune system attacks fetal platelets, leading to dangerously low platelet levels before and/or after birth. in a previous pregnancy can also increase the risk of severe FNAIT in subsequent pregnancies.
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The main diagnostic laboratory tests for FNAIT are:
- Platelet antibody testing, which identifies the maternal antibodies that react against the baby’s platelet markers.
- HPAHuman platelet antigen Proteins found on the surface of platelets. Incompatibility between maternal and fetal human platelet antigens can trigger FNAIT. genotypingGenotyping A laboratory test that identifies which platelet antigens a person carries. Often used to confirm HPA incompatibility and assess recurrence risk., which identifies the platelet antigens carried by the mother, father, and baby to determine whether the baby inherited an antigen that the mother does not have.
- Crossmatching, which mixes maternal serum with paternal platelets to check whether the mother’s antibodies react against them.
The names of the tests and the numbers in your results can sound a little too complex and confusing, but with a little preparation, you can make the most of your consultation.
Gather relevant medical information
Before the consultation, collect any available information related to your current and previous pregnancies. You should have some discharge documents and exams, such as prenatal ultrasound reports or the baby’s blood count results.
If you have had a previous pregnancy affected by FNAIT, maybe you still have some documents that report the clinical manifestations, their severity, and when they occurred. Previous HPA antibody or genotyping results are important information when assessing FNAIT risk.
Reports about treatments given during pregnancy or after delivery are useful as well.
Read more about FNAIT testing and diagnosis
What your results can tell you
Besides providing information about the case being investigated, testing can help estimate the likelihood that future children will be affected by the same issue.
The father’s results help guide this estimate. The father has two copies of the gene that determines the HPA type. Let’s call one copy A and the other B.
The baby inherits one copy from the mother and one from the father. In our example, the mother has antibodies against the HPA associated with A.
If the father is A/A, every baby will inherit A from him, so all pregnancies will be at risk of FNAIT.
If the father is A/B, each baby has a 50% chance of inheriting A and a 50% chance of not inheriting it. Paternal HPA genotyping can therefore help estimate the risk in a future pregnancy.
If the baby does not inherit A, the mother’s antibodies against that HPA will not target the baby’s platelets.
Why isn’t everyone tested for this during pregnancy?
Routine screening for FNAIT is not currently part of standard prenatal care. One reason is that finding an HPA incompatibility or maternal antibodies does not reliably predict which babies will develop severe FNAIT.
Screening everyone could therefore lead to unnecessary monitoring or treatment in many pregnancies. Researchers are still studying how to better identify pregnancies that are truly at high risk.
Prepare questions for the consultation
Writing down questions beforehand can help you organize your thoughts and remember to address all your concerns. Here are some questions that could be helpful:
- What did my platelet-immunology results show?
- Was a specific HPA antibody identified?
- Do my partner or baby need additional testing?
- Are there any additional tests recommended for me?
- What do these findings mean for my current pregnancy?
- Could these results affect a future pregnancy?
If you do not understand a test name or result, ask for it to be explained in plain language.
What happens after the consultation?
Platelet-immunology results are interpreted together with clinical information, such as pregnancy history, the baby’s platelet counts and symptoms. The clinical history and laboratory findings are considered together when evaluating FNAIT.
Depending on the findings, further testing could be recommended. Laboratory results can help support the diagnosis and assess whether a future baby may be at risk, but there is currently no established laboratory test that can reliably predict the severity of thrombocytopenia or whether intracranial hemorrhage will occur.
