Human Platelet Antigen 1 (HPA-1) Genotype Biomarker Testing
It identifies your HPA-1 genetic type to assess platelet antigen compatibility risks, with convenient ordering and Quest-based lab collection via Vitals Vault.
With Vitals Vault, you have access to a comprehensive range of biomarker tests.
This test reports your Human Platelet Antigen 1 (HPA-1) genotype, which is a genetic “type” on the surface of platelets. It does not measure how many platelets you have or how well they function.
HPA-1 genotyping is mainly used when a clinician is evaluating platelet antigen incompatibility, such as suspected fetal/neonatal alloimmune thrombocytopenia (FNAIT/NAIT) or a history of platelet transfusion refractoriness. In those settings, knowing whether you are HPA-1a/a, HPA-1a/b, or HPA-1b/b can guide next steps.
Because it is a genotype, your result typically does not change over time. The value comes from pairing it with the right clinical history and, when appropriate, antibody testing.
Do I need a Human Platelet Antigen 1 Genotype test?
You may be a good candidate for HPA-1 genotyping if you or your clinician are trying to explain a platelet-related compatibility problem rather than a general bleeding or clotting symptom. Common scenarios include a newborn with unexpectedly low platelets, a prior pregnancy affected by suspected FNAIT, or a plan for a future pregnancy where platelet antigen incompatibility is a concern.
This test can also be considered if you have had poor responses to platelet transfusions (for example, platelet counts that do not rise as expected), especially when alloimmunization is suspected. In that situation, HPA typing can help a transfusion service select better-matched platelet products.
If your main question is “Why is my platelet count low or high?” this is usually not the first test to order. A complete blood count (CBC), review of medications, and evaluation for immune or bone marrow causes are typically more informative.
Genotyping supports clinician-directed care and transfusion or pregnancy planning, but it is not a standalone diagnosis and should be interpreted alongside your history and related lab findings.
HPA-1 genotyping is typically performed in a CLIA-certified laboratory using DNA-based methods; results should be interpreted in clinical context and do not diagnose a condition by themselves.
Lab testing
Order Human Platelet Antigen 1 (HPA-1) Genotype testing through Vitals Vault.
Schedule online, results typically within about a week
Clear reporting and optional clinician context
HSA/FSA eligible where applicable
Get this test with Vitals Vault
If you already know HPA-1 genotyping is part of your workup, Vitals Vault lets you order the test and complete your blood draw through a nationwide lab network. Your report is delivered in a format you can share with your clinician or transfusion team.
Because HPA-1 is a genetic result, the most helpful “next step” is often interpretation: what your genotype implies for compatibility risk, and which follow-up tests (such as platelet antibody testing) actually answer your clinical question. PocketMD can help you turn the lab report into a focused set of questions for your OB/GYN, hematologist, or transfusion medicine specialist.
If you are comparing options, ordering through Vitals Vault can also make it easier to keep results organized in one place for future pregnancies, procedures, or transfusion planning.
- Order online and complete collection at a Quest location
- Clear, shareable results for your clinician or transfusion service
- PocketMD guidance to plan sensible follow-up testing
Key benefits of Human Platelet Antigen 1 Genotype testing
- Clarifies whether you carry HPA-1a and/or HPA-1b, which can matter for platelet antigen compatibility.
- Supports evaluation of suspected fetal/neonatal alloimmune thrombocytopenia (FNAIT/NAIT) when paired with clinical history.
- Helps guide follow-up testing, such as anti-HPA-1a antibody assessment, when incompatibility is suspected.
- Can inform transfusion planning in cases of suspected platelet alloimmunization or poor platelet transfusion response.
- Provides a stable, lifelong genetic result that typically does not require repeat testing.
- Improves communication with specialists by giving a concrete genotype result rather than a vague “compatibility concern.”
- Keeps your result accessible for future care decisions, with optional PocketMD support to interpret it in context.
What is Human Platelet Antigen 1 (HPA-1)?
Human Platelet Antigen 1 (HPA-1) is a platelet surface antigen system determined by a common genetic variation in the ITGB3 gene (which encodes part of the platelet glycoprotein receptor complex). The two main forms are HPA-1a and HPA-1b.
Your “HPA-1 genotype” describes which versions you inherited: HPA-1a/a, HPA-1a/b, or HPA-1b/b. This matters because if a person lacks an antigen (for example, HPA-1a negative) and is exposed to it through pregnancy or transfusion, their immune system may form antibodies against that antigen.
Those antibodies can cross the placenta and affect a fetus’s platelets (FNAIT), or they can interfere with platelet transfusions by destroying transfused platelets. The genotype alone does not prove antibodies are present; it tells you whether an incompatibility is possible and helps target the right antibody testing.
Genotype vs antibody testing
Genotyping tells you what antigens you can express. Antibody testing tells you whether your immune system has reacted to an antigen you do not have. In real-world care, clinicians often use both: genotype to assess compatibility and antibody tests to confirm immune-mediated risk.
Why HPA-1 is emphasized
Several platelet antigen systems exist, but HPA-1 is one of the most clinically important in many populations because anti-HPA-1a antibodies are a common cause of FNAIT. Your clinician may still consider additional HPA types depending on the case.
What do my Human Platelet Antigen 1 Genotype results mean?
“Low” result: HPA-1a negative (HPA-1b/b)
For a genotype test, “low” is best thought of as lacking HPA-1a (often reported as HPA-1b/b). This can be clinically relevant because HPA-1a negative individuals can form anti-HPA-1a antibodies after exposure through pregnancy or transfusion. If there is a history suggestive of FNAIT or transfusion refractoriness, your clinician may order platelet antibody testing and consider compatibility planning. On its own, HPA-1b/b does not mean you currently have antibodies or that a complication will occur.
In-range/expected result: HPA-1a present (HPA-1a/a or HPA-1a/b)
If your result shows HPA-1a/a or HPA-1a/b, you have the HPA-1a antigen. This generally lowers concern for anti-HPA-1a–mediated incompatibility because you are unlikely to form antibodies against an antigen you already have. However, it does not rule out other platelet antigen incompatibilities or other causes of low platelets in a newborn or poor transfusion response. Your clinician may still evaluate other HPA systems or non-immune causes depending on the situation.
“High” result: not applicable in the usual way for genotyping
Genotype tests do not have “high” values like hormones or nutrients. Instead, results are categories (a/a, a/b, or b/b). If your report includes additional flags, they usually relate to test quality (for example, an indeterminate call) rather than a “high” biological level. If the result is indeterminate, a repeat specimen or confirmatory testing may be recommended.
Factors that influence HPA-1 interpretation
Because HPA-1 is genetic, your genotype is not meaningfully changed by diet, fasting, illness, or most medications. What does change your risk is exposure history, such as pregnancy, transfusion, or transplant, because exposure can lead to antibody formation if you lack an antigen. Your clinical context also matters: a newborn’s platelet count trend, maternal antibody results, and transfusion response patterns often determine whether this genotype is actionable. Rarely, lab factors like sample mix-ups, low DNA yield, or technical limitations can lead to an inconclusive result.
What’s included
- Hpa 1 Pla Genotype
Frequently Asked Questions
What does an HPA-1 genotype test show?
It shows which HPA-1 variants you carry—HPA-1a and/or HPA-1b—reported as HPA-1a/a, HPA-1a/b, or HPA-1b/b. This helps assess whether platelet antigen incompatibility is possible in pregnancy or transfusion settings.
Is HPA-1 genotyping the same as a platelet count?
No. A platelet count (from a CBC) measures how many platelets are in your blood. HPA-1 genotyping is a DNA test that identifies a platelet antigen type and does not tell you whether your platelet count is low or high.
Do I need to fast for an HPA-1 genotype test?
Fasting is not typically required because this is genetic testing from a blood sample. If your draw is bundled with other labs that do require fasting, follow the instructions for the full panel.
If I am HPA-1b/b, does that mean I have antibodies?
Not necessarily. HPA-1b/b means you are HPA-1a negative, which can allow anti-HPA-1a antibodies to form after exposure, but it does not prove antibodies are present. Antibody testing is needed to determine whether you have developed anti-HPA-1a.
How often should I repeat HPA-1 genotyping?
Usually you do not need to repeat it because your genotype does not change. Repeat testing is mainly considered if a result is indeterminate or if there is a concern about specimen or identity issues.
Can this test diagnose FNAIT (neonatal alloimmune thrombocytopenia)?
No. It can support an evaluation by showing whether antigen incompatibility is possible, but diagnosis typically depends on the newborn’s platelet findings plus maternal antibody testing and clinical assessment.
What other tests are commonly ordered with HPA-1 genotyping?
Depending on the case, clinicians may add platelet antibody testing (such as anti-HPA-1a), broader HPA typing, and a CBC for the affected patient (often the newborn). In transfusion scenarios, HLA antibodies and platelet crossmatching may also be considered by the transfusion service.