Hemophilia carrier testing: Who should get screened and why?

Many carriers of hemophilia don’t have symptoms and may not even be aware they have the gene, but there’s still a chance they can pass it on to their children. That’s why carrier screening is often recommended, as it helps you make informed decisions about your health and family planning. Understanding your carrier status can provide clarity, comfort, and control.

Hemophilia carrier testing can tell you if you carry the gene variant linked to this rare blood disorder, enabling you to take proactive steps for your future. 

Although different screening options are available to determine your carrier status, research shows that genetic testing offers the most accurate and comprehensive results. 

In this article, we’ll cover everything you need to know about hemophilia carrier testing, why it matters, and the available screening options you can consider. 

Hemophilia and its types explained 

Hemophilia is a rare condition that affects the blood’s ability to clot properly. While that might sound serious, understanding how it works can help you feel more in control and aware of your options. 

This condition occurs when you don’t have enough clotting factor — a protein needed to stop bleeding. People with hemophilia usually experience prolonged bleeding from minor injuries, frequent nosebleeds, easy bruising, and, in severe cases, spontaneous internal bleeding in joints and organs.

The type of hemophilia you may have depends on which clotting factor is missing:

• Hemophilia A: Caused by a deficiency in clotting factor VIII (Factor 8). According to the Center for Disease Control and Prevention (CDC), it’s three to four times more prevalent than other forms of hemophilia.

• Hemophilia B: Caused by a deficiency in clotting factor IX (Factor 9).

• Hemophilia C: A very rare form of hemophilia caused by a deficiency in clotting factor XI (Factor 11).

Hemophilia primarily affects men, but women can be carriers and may also experience symptoms. According to the CDC, hemophilia symptoms in women are often less severe than in men, but if a woman has clotting factors below 40%, she can experience moderate to severe symptoms.

Doctors also classify hemophilia as mild, moderate, or severe based on the levels of clotting factor present in the blood:

The good news is that with the right knowledge and support, people with hemophilia and carriers can lead healthy lives and plan pregnancies safely.

How is hemophilia passed down?

Most cases of hemophilia are inherited, but in rare cases, you may develop acquired hemophilia, where the immune system mistakenly attacks clotting factors, causing excessive bleeding. 

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That said, hemophilia primarily affects people assigned male at birth (AMAB), and the reason lies in genetics. It’s an X-linked disorder, meaning the gene responsible for hemophilia is located on the X chromosome.

Here’s how it works:

• Humans typically have two sex chromosomes: XX for those assigned female at birth (AFAB) and XY for those AMAB.

• You inherit one X chromosome from your mother and either an X or Y chromosome from your father.

• If you’re AFAB and inherit a mutated X chromosome, your other healthy X chromosome can compensate, making you a carrier rather than developing hemophilia.

• If you’re AMAB and inherit an X chromosome with the mutation, you don’t have a second X to compensate, so you’ll develop hemophilia.

The table below simplifies how you may pass hemophilia to your children depending on your carrier status:

While these possibilities can seem overwhelming, timely genetic testing and counseling can help shed light and inform you on the next steps.

Why are women screened for hemophilia more often?

Hemophilia carrier testing is primarily done on women because they are the most likely carriers of the hemophilia gene. Since women have two X chromosomes, they can inherit the mutated gene without developing the condition themselves.

However, this doesn’t mean female carriers are completely unaffected. Some carriers can experience symptoms like:

• Heavy or prolonged menstrual bleeding

• Easy bruising and frequent nosebleeds

• Excessive bleeding after surgery, childbirth, or dental work

These individuals are known as symptomatic carriers, and with the right guidance, the symptoms can be managed effectively. 

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On the other hand, those with levels above 40% who have no symptoms of the condition but still have the mutated X gene are known as asymptomatic carriers. 

Hemophilia carriers are typically classified as obligate or possible carriers based on their family history. See what the differences are in the table below:

Bonus read — Learn more about other types of genetic screening in our guides below:

• Cystic fibrosis carrier screening 

• Genetic testing for a muscular dystrophy carrier

• Prenatal genetic testing 

• NIPT test

When is hemophilia carrier testing recommended?

Source: Paul Danilyuk

It’s not always easy to think about genetic risks, especially when you feel fine, but testing can give you peace of mind and a clear plan. Since many carriers don’t experience symptoms, hemophilia carrier testing is typically recommended for the following reasons:

1. Family history of hemophilia

2. Pregnancy planning

3. Unexpected bleeding or upcoming medical procedures

1. Family history of hemophilia 

If hemophilia runs in your family, testing can help determine whether you’re a carrier. You would typically be advised to get tested if:

• You have a male relative (such as a father, brother, or uncle) with hemophilia

• Your mother is a known carrier of the hemophilia gene

• There’s a history of unexplained bleeding disorders in your family

You should also consider getting tested for the condition if your child is diagnosed with hemophilia or identified as a carrier, especially if the father doesn’t have hemophilia. 

2. Pregnancy planning

Knowing your carrier status before pregnancy allows you to assess the likelihood of passing hemophilia to your child. If you test positive, you can discuss reproductive options, prenatal testing, and delivery precautions with your doctor to ensure the best care for both you and your baby.

Also, if you’re already pregnant, you can still get tested to know your carrier status so you can understand the possibilities of your child inheriting the conditions and learn the next steps to take.

3. Unexplained bleeding or upcoming medical procedures

Although many carriers don’t show symptoms, some may experience excessive bleeding, easy bruising, or prolonged menstrual periods. 

If you’ve had frequent nosebleeds, excessive bleeding after injuries, or unusually heavy periods, testing can help determine if you’re a symptomatic carrier.

Additionally, if you’re scheduled for surgery, dental work, or any medical procedure that could involve bleeding, knowing your carrier status allows doctors to take extra precautions to minimize risks. Even if you don’t have hemophilia, being a carrier can sometimes impact blood clotting.

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Screening options for hemophilia carrier testing

There are two primary ways to determine whether you’re a hemophilia carrier. While both methods provide valuable insights, they differ in accuracy.

1. Clotting factor assay

This test measures the activity levels of clotting factors VIII (for hemophilia A) or IX (for hemophilia B) in your blood. You may be classified as a carrier if your clotting factor levels fall below 40%. 

However, studies have shown that this method has some limitations:

1. Many carriers have normal clotting levels. Around 80% of carriers have factor levels above 40%, meaning the test could miss them entirely.

2. Factor VIII levels fluctuate. Pregnancy, birth control, and other factors can artificially raise factor VIII activity, making the test less reliable for identifying carriers of hemophilia A.

The accuracy of clotting factor assays is about 80 to 90%, and as such, it isn’t considered the most precise way to confirm your carrier status. That’s why many people turn to genetic testing, as it offers more clarity and peace of mind.

2. Genetic testing 

Based on research, genetic testing is often considered the gold standard for finding out if you’re a hemophilia carrier. Genetic testing directly examines your DNA for variants in the F8 (hemophilia A) or F9 (hemophilia B) genes rather than relying on clotting activity. Depending on the technology used, this method can detect mutations with 90 to 99% accuracy.

Whole-genome sequencing (WGS) is the most comprehensive method for analyzing your DNA, which is the genetic testing method used by Nucleus Family. 

Unlike traditional tests that check for a few conditions, Nucleus’ test examines your entire genome to provide a full picture of your genetic profile. This lets you identify your hemophilia carrier status and hundreds of other inheritable conditions you can unknowingly pass on to your children. Learn more about it and sign up below. 

What to do if you’re a hemophilia carrier

Source: Cottonbro Studio

Learning that you’re a hemophilia carrier can be stressful, but it’s an important first step. You can consider the following routes to take control of the situation, protect your health, and make the right choices for your future family:

1. Talk to a genetic counselor and your healthcare provider

2. Protect yourself from bleeding risks

3. Understand your reproductive options 

1. Talk to a genetic counselor and your healthcare provider

A genetic counselor can help you fully understand your carrier status, including the chances of passing hemophilia to your children. 

If you’re planning a pregnancy, they can also guide you through potential risks, such as an increased likelihood of postpartum bleeding, and discuss available medical options.

Your doctors should also know your carrier status, whether it’s a routine dental procedure, surgery, or even childbirth. This allows them to take necessary precautions to prevent excessive bleeding and manage your care safely.

2. Protect yourself from bleeding risks

Even if you don’t have hemophilia yourself, some carriers (especially symptomatic ones) can be more prone to bruising or excessive bleeding. It’s generally recommended to avoid contact sports like football, hockey, or boxing, which could lead to severe injuries.

You should also avoid certain medications that can interfere with blood clotting and worsen bleeding, such as some pain relievers, like aspirin and ibuprofen. If you need pain relief, your doctor can recommend safer alternatives that won’t put you at risk.

3. Understand your reproductive options 

If you’re diagnosed as a carrier and are worried about passing the condition on to your children, you can consider other conception options like in vitro fertilization (IVF) with pre-implantation genetic diagnosis. This will enable you to check which of your embryos have hemophilia or are carriers, so you can make informed decisions about which ones to transfer.

If you’re already pregnant and have been identified as a hemophilia carrier, you can still consider doing a prenatal diagnosis test like amniocentesis. 

This test can check to see if your baby has hemophilia or is a carrier, so you can prepare ahead. However, such tests are invasive, and you should discuss the risks and benefits with your healthcare provider before taking them. 

Nucleus: Comprehensive genetic screening for hemophilia and 900+ conditions

Rather than screening for hemophilia alone, getting a more comprehensive genetic panel can be beneficial as it would provide information on your carrier status for many other conditions. Nucleus Family offers this using whole-genome sequencing — the most advanced genetic testing technology today. 

Nucleus Family’s WGS test screens for over 900 conditions, making it a great source of information if you’re planning for parenthood or simply want a clearer picture of your genetic health.

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This clinical-grade, physician-approved test is a comprehensive screening tool for hemophilia and other inherited conditions, allowing you to make informed reproductive and health decisions.

Nucleus also helps you act on your genetic risks. If your carrier status is confirmed, Nucleus AI provides personalized health recommendations, such as avoiding certain medications, adjusting physical activities, or making lifestyle changes to support your health.

To ensure you fully understand your results, the platform also offers genetic counseling through a partnership with SteadyMD, where you can speak with certified genetic counselors about your risks, family planning, or medical precautions.

Take control of your health with Nucleus

Nucleus’ test kit is available for just $399, and this price includes everything you need, from the testing kit and two-way shipping to comprehensive reports on your genetic health. 

Taking the first step toward a more informed parenthood journey is simple:

1. Sign up for Nucleus Family

2. Provide your personal information

3. Order your kit

Each kit comes with instructions on how to collect your sample using the provided cheek swabs. Once your sample reaches the lab, your results will be processed and sent in 6–8 weeks, giving you invaluable insights into your genetic health.

Take the first step toward informed health and reproductive decisions by starting with Nucleus today.

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Feature image source: Cedric Fauntleroy