The standard blood test used to spot fetal and neonatal alloimmune thrombocytopenia (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.) can sometimes miss the antibodies causing the problem, as shown by a recent case report presented at the 2026 International Society on Thrombosis and Haemostasis (ISTH) Congress and published in Research and Practice in Thrombosis and Haemostasis.
In FNAIT, the mother’s immune system makes fighter cells called antibodies that cross the placenta and attack the baby’s platelets, the tiny blood pieces that help stop bleeding. In this case, the mother had made three different attacking antibodies at once, something doctors rarely see.
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Yet one common test, called MAIPA (Monoclonal Antibody-specific Immobilization of Platelet Antigens), kept coming back normal again and again during the pregnancy. Only a second kind of test, called Luminex, detected the harmful antibodies.
“This case underlines the necessity of using complementary methods, particularly when standard MAIPA assays fail to detect clinically relevant alloantibodies,” the authors said.
Read more about FNAIT testing and diagnosis
The 34-year-old mother had already had one baby born with low platelets, caused by two antibodies made by her immune system (known as anti-HPAHuman platelet antigen Proteins found on the surface of platelets. Incompatibility between maternal and fetal human platelet antigens can trigger FNAIT.-1a and anti-HPA-3a) that attacked the baby’s platelets. This put future babies at higher risk as well.
During her second pregnancy in 2024, doctors started checking her at 17 weeks and began IVIGIntravenous immunoglobulin A treatment given to pregnant women with a history of FNAIT or known alloantibodies. IVIG reduces the immune reaction against fetal platelets. (intravenous immunoglobulinIntravenous immunoglobulin A treatment given to pregnant women with a history of FNAIT or known alloantibodies. IVIG reduces the immune reaction against fetal platelets.) treatment, a therapy that calms down the immune system, at 20 weeks.
The MAIPA test did not find any antibodies, but a Luminex-based test clearly found two. About a month before delivery, a third type of antibody (anti-HPA-5b) appeared and finally showed up on both tests.
In June 2025, a baby boy was born almost at full term. His platelet levels were slightly low at birth but were back to normal by day two.
