Thrombosis and Thrombophilia

What is thrombosis?

The tubes that carry blood throughout the body are called blood vessels. When a blood vessel is damaged, blood cells called platelets stick together to form blood clots. A scab that forms over a cut in the skin is a type of clot.

Thrombosis (thrahm-BO-sis) happens when a blood clot forms in a blood vessel. Most of the time, clotting is a normal, healthy process that stops bleeding.

But clots can cause problems if they:

  • Form when they are not needed for healing or grow beyond the damaged area
  • Do not dissolve when they are no longer needed
  • Are big enough to block blood flow in a blood vessel

What is thrombophilia?

Some people’s blood is more likely to form clots. This is called thrombophilia (thrahm-bo-FIL-ee-uh).

If your child has thrombophilia, they may have: 

  • Frequent clots in blood vessels
  • Clots in an unusual place (like blood vessels in the liver, kidney or brain)
  • What causes blood clots?

    A blood clot can form any time there is bleeding inside the body. The chance of clots forming in blood vessels may be higher for these reasons:

    • If a child has a central line inserted into a vein for treatment.
    • After major injury or surgery, because the body’s clotting system may be especially active.
    • Changes (mutations) in 1 or more genes that carry instructions for 1 of the substances that control clotting. The abnormal gene is passed down from a parent to a child.
    • Lupusinflammatory bowel diseasenephrotic syndrome and some local infections can make the body more likely to form blood clots.
    • Lack of activity reduces blood flow and increases the chance of a clot forming in a vein deep in the body. This is called deep vein thrombosis (DVT) and mostly affects the lower legs. DVT may happen if illness or treatment limits your child’s movement, such as having a cast to heal a broken bone. Long airplane trips and car rides also limit activity and can increase the risk of DVT.
    • Use of birth control that contains the hormone estrogen. Pregnancy also increases clotting.
  • Serious problems clots may cause

    Any time a clot forms inside the body, there is a chance that it may block blood flow through a blood vessel. This can happen if:

    • The clot is big enough
    • A clot breaks free from where it formed, flows through the bloodstream and blocks a blood vessel

    Blocking blood flow can be serious – even deadly – if a clot blocks certain vessels:

    • In the lungs
    • To the brain
    • To the heart

Thrombosis at Seattle Children’s

The doctors at our Cancer and Blood Disorders Center are experts at diagnosing and treating blood clots. Our experience helps:

  • Find the cause
  • Provide the right treatment
  • Prevent your child from getting more clots 

If you would like an appointment, ask your primary care provider to refer you. If you have a referral or would like a second opinion, contact the center at 206-987-2106.

Providers, see how to refer a patient.

  • The experts you need for complete care

    Our doctors are nationally known for treating children who have blood disorders. The doctors who will guide your child’s care are board-certified in pediatric oncology-hematology. This means they are approved to give the special care your child needs and they constantly expand their knowledge about blood disorders.

    We keep a careful watch on your child’s health and provide treatment as needed. We offer a full range of medicines to prevent and treat blood clots. Our doctors stay abreast of new treatments being developed and take part in clinical trials of new options. The right treatment at the right time will have the best results for your child and your family.

    If your child is treated with blood thinners, (anticoagulants), our specially trained pharmacists work with you and your child to monitor the safety of their treatment. We help you find the closest and most convenient lab for follow-up testing to check how well your child’s blood is clotting. Few children’s hospitals offer this service.

    We care for your whole child. Your family has a full team behind you, including doctors, nurses, social workers and other specialists as needed. Read more about the supportive care we offer.

  • Among the nation’s best children’s hospitals

    Our specialty is treating children’s conditions while helping them grow up to be healthy and productive. Our physician-scientists help set national standards for care of young people with blood disorders.

    Children do not react to illness, injury, pain and medicine in the same way as adults. They need – and deserve – care designed just for them. Our experts focus on how treatments today affect growing bodies in the future. We plan your child’s treatment based on years of experience and the newest research on what works best – and most safely – for children.

  • Support for your whole family

    Having a child with a clotting problem can be stressful. If your child has a clot that is causing problems, we will see them in our clinic or emergency department that same day. Some children need to stay overnight in the hospital for treatment. If needs are not urgent, new patients can be seen in 1 or 2 weeks.

    During visits, we take time to explain your child’s condition. We help you fully understand your treatment options and make the choices that are right for your family.

    Our child life specialists and social workers help your child and your family through the challenges of this condition. We connect you to community resources and support groups.

    At Seattle Children's, we work with many children and families from around the Northwest and beyond. Whether you live nearby or far away, we can help with financial counseling, schooling, housing, transportation, interpreter services and spiritual care. Read about our services for patients and families.

Symptoms of Thrombosis and Thrombophilia

The symptoms of a blood clot in a blood vessel depend on:

  • Where the clot is
  • If the blood vessel is totally or partly blocked

Clots in blood vessels deep in the body (DVT) mainly affect the lower leg, with pain and swelling. Sometimes this feels like a pulled muscle.  Clots in veins closer to the surface of the skin may cause the area to be warm, red and painful.

Clots in a lung may cause:

  • Breathing problems
  • Chest pain
  • Cough
  • Coughing up blood
  • Fainting and tiredness

Sometimes when a child gets a tube (catheter) inserted in a vein, it can irritate the inside of the blood vessel and cause a clot.

  • A serious clot is more likely with some types of intravenous (IV) lines, such as a central line or PICC line.
  • Symptoms depend on where the clot is and how much of the blood vessel is blocked.
  • Your child may have pain and swelling at the site of the clot or more general swelling of an arm or leg.

If your child has thrombophilia, they may have:

  • Frequent clots in blood vessels
  • Clots in an unusual place (like the liver, kidney or brain)

Diagnosing Thrombosis and Thrombophilia

We check for and ask about any symptoms, past or present, that suggest a possible clot.

Next, the doctor will:

  • Do a physical exam to look for signs of clots (such as redness or swelling in a leg or arm)
  • Check your child’s heart and lungs by listening with a stethoscope
  • Measure their blood pressure
  • Do imaging studies as needed
  • Less often, do a blood test (D-dimer) to learn more about a clot, like if it is newly formed or might change size or location
  • Imaging tests

    If the doctor suspects a clot, your child will have imaging studies to find the clot and get information about it. The tests may include:

    • Ultrasound that uses sound waves to show blood flowing through the blood vessels
    • CT angiogram of the chest to look for clots in the lung
    • CT (computed tomography) scans of blood vessels
    • An image of the heart made with sound waves (echocardiogram)
    • MRI (magnetic resonance imaging) scans of the head to check for clots in the brain
    • Special X-rays that help show blood flow in vessels (venogram
  • Finding the cause of your child’s clots

    Doctors will look for and treat the underlying cause of your child’s clot.

    Our doctors will work with your family to decide if genetic testing for thrombophilia is needed. We consider if the results would change how we treat your child and whether other family members have been diagnosed with thrombophilia.

    An inherited condition may cause your child to have:

    • Frequent blood clots
    • Clots in unusual places
    • A stroke

Treating Thrombosis and Thrombophilia

Some children with blood clotting problems only need treatment for a short time. Others may need lifelong treatment. Treatment depends on:

  • What is causing the clot
  • How severe the clot is
  • If it is your child’s first clot

Your child's doctor will talk with you about the best way to care for your child's condition, including any new treatment options offered in research studies. Then you can decide whether you want to take part. We will work with your child's other doctors to coordinate care.

The goal is to stop the blood clot from getting bigger and to let your child’s natural clot-dissolving ability shrink the clot. Stopping the clot from growing lowers the chance that it will break free and move to the lungs, heart or brain.

In recommending treatment, we consider:

  • If your child’s health is stable or changing quickly
  • Their risk of bleeding
  • Whether they are likely to need surgery that could increase the risk of a clot 

After starting treatment, we keep a careful watch on your child. This includes imaging studies to check the size of the clot in 6 weeks to 3 months.

  • Blood thinners (anticoagulants)

    Blood thinners reduce the blood's ability to clot. These medicines also stop existing blood clots from getting bigger. But they do not break up blood clots that have already formed. These medicines are also called anticoagulants (AN-te-ko-AG-u-lants).

    Our team will carefully assess your child to decide the best medicine for them. How we treat clots in children has been changing as we learn more about newer medicines. Most children stay at the hospital overnight at the start of treatment for a new clot. During this time, we watch closely to see how the treatment is working. We teach parents about giving injections if needed.

    Common blood thinners (anticoagulants) are:

    • Enoxaparin (Lovenox), given by injection.
    • Rivaroxaban (Xarelto), in pill form.
    • Apixaban (Eliquis), in pill form.
    • Warfarin (Coumadin), in pill form.
    • Heparin. Doctors use this medicine if the clot needs quick treatment because of its size or location or if your child is scheduled for surgery. Your child would stay in the hospital for treatment.

    It is important to get the right amount of medicine so your child’s blood is not too thin. We tell you warning signs and regularly check how well your child’s blood is clotting. For families who do not live in the Seattle area, our specially trained pharmacists help you find the closest lab for blood testing. Less need for follow-up lab tests is a benefit of newer medicines (rivaroxaban and apixaban).

  • Breaking up clots

    Many blood clots dissolve on their own. But your child may need treatment if they have a large blood clot that is causing problems. Your doctor or specialists called interventional radiologists may break up a blood clot using 1 or more of these methods:

    • Use medicines to quickly dissolve it. These are called thrombolytic agents. Because they increase the risk of bleeding, we use thrombolytics only for clots that are severe or life-threatening.
    • Use a tool to break up the clot and suck it out.
    • Stretch the blood vessel to make it wider (angioplasty) using a tube placed in the blood vessel.
  • Preventing clots

    We help prevent blood clots when children have factors that make it more likely clots will form, like a central line or active inflammatory bowel disease.

    If your child has thrombophilia, we can help even if they have never had a clot by:

    • Checking your child's risk for a clot based on things like illness, infection, upcoming surgery and medicines they take.
    • Helping you decide about genetic testing.
    • Suggesting steps to reduce the chance of clots in high-risk situations. These include surgery, wearing a cast for a broken bone or long trips in planes or cars.
    • Talking about options for birth control that do not contain estrogen, which increases the risk of clots.
    • Giving you information about thrombophilia and ways to prevent clots, like avoiding long periods of sitting.

    Rarely, preventing a clot includes taking medicines that help stop blood clots from forming (thrombin inhibitors). These medicines are only used for children in special situations, most often in the Intensive Care Unit (ICU).

Contact Us

If you would like an appointment, ask your primary care provider to refer you. If you have a referral or would like a second opinion, contact the center at 206-987-2106.

Providers, see how to refer a patient.

Paying for Care

Learn about paying for care at Seattle Children’s, including insurance coverage, billing and financial assistance.

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