Flow cytometry tests are used to confirm a diagnosis of 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.).
A flow cytometry test is a non-invasive, lab-based test used in combination with other diagnostic tools in both pregnancy and post-delivery. It works by testing the mother’s serum, found in the blood, for antibodies against human platelet antigens (HPAs) on the baby’s platelets, inherited from the father.
Learn more about FNAIT testing and diagnosis
What is flow cytometry in FNAIT?
In FNAIT, flow cytometry involves analyzing the platelets in a blood sample from the father combined with the blood serum of the mother using a laser. The serum is the liquid part of the blood that holds antibodies, hormones, electrolytes and other proteins.
A fluorescent dye is added, and if the mother has antibodies, they will bind to the father’s platelets and show a fluorescent signal.
During pregnancy
Flow cytometry is used when FNAIT is suspected or when FNAIT has occurred in previous pregnancies. It detects maternal antibodies against fetal HPAs and guides treatment during pregnancy, including the use of 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. (IVIGIntravenous immunoglobulin A treatment given to pregnant women with a history of FNAIT or known alloantibodies. IVIG reduces the immune reaction against fetal platelets.) and steroids.
After birth
Flow cytometry helps distinguish FNAIT from other potential causes of neonatal thrombocytopeniaNeonatal thrombocytopenia Low platelet count in a newborn. In FNAIT, platelet levels may drop dangerously low within hours after birth. and guide treatment choices for the newborn, such as platelet transfusions.
Benefits of flow cytometry
Flow cytometry is part of the FNAIT diagnostic toolkit. It plays a role in diagnosing FNAIT in fetuses and newborns and has the following benefits:
- Reduces the risk to the fetus or newborn as it is non-invasive.
- Guides treatment and allows for proactive medical intervention by confirming a diagnosis of FNAIT.
- Informs prenatal management of subsequent pregnancies.
Other diagnostic tools used in FNAIT
As well as flow cytometry, an accurate diagnosis of FNAIT requires several diagnostic tools including:
Fetal ultrasound: checks for bleeding, 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. or swelling in the fetus that may indicate hydrops fetalis.
MAIPA (Monoclonal Antibody Immobilization of Platelet Antigens) assay: identifies the exact platelet antibodies following flow cytometry screening.
Paternal genotypingPaternal genotyping Testing the father’s blood to determine which HPAs may have been passed to the fetus.: to determine if the father has HPAs that the mother lacks.
Non-invasive fetal genotypingGenotyping A laboratory test that identifies which platelet antigens a person carries. Often used to confirm HPA incompatibility and assess recurrence risk.: done via cell-free fetal DNA testing.
Platelet cross-matching: compares paternal platelets and maternal serum to check for incompatibility
Physical symptoms in the newborn: such as bruising, petechiae and purpura, as well as low platelet counts and ultrasounds to detect intracranial hemorrhage.
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