Heart and Blood Conditions

Thrombosis and Thrombophilia

What is thrombosis?

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 aren’t needed for healing or grow beyond the damaged area
  • Don’t 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)

  • A blood clot can form in a blood vessel any time there’s 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.
    • Lupus, inflammatory bowel disease, nephrotic 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.

  • 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 a vessel:

    • In the lungs (pulmonary embolism)
    • To the brain (stroke)
    • To the heart (heart attack)

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

Please contact the center at 206-987-2106 for more information, a second opinion or to make an appointment.

  • Our doctors are nationally known for treating children who have blood disorders. The doctors who guide your child’s care have special training in how to diagnose and treat children with blood conditions. They constantly expand their knowledge about blood disorders in children (pediatric hematology).

    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 (anticoagulants). The right treatment at the right time will have the best results for your child and your family.

    If your child is treated with 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.

  • Our specialty is treating children’s conditions while helping them grow up to be healthy and productive. U.S. News & World Report consistently ranks Seattle Children’s among the nation’s best children’s hospitals. We rank #1 in the Northwest and are the only pediatric medical center in Washington state to be ranked.

    Children don’t react to illness, injury, pain and medicine in the same way as adults. They need – and deserve – care designed just for them.

    Our experts base their treatment plans on years of experience and the newest research on what works best – and most safely – for children.

  • 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
  • Whether 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

Clots in veins closer to the surface of the skin:

  • May cause the area to be warm, red and painful
  • May cause a fever

Clots in the lung may cause:

  • Breathing difficulty
  • 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 significant clot is more likely with a central line or PICC line than with other types of intravenous (IV) lines.
  • Symptoms depend on where the clot is and how much it fills the blood vessel.
  • 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 blood vessels in the liver, kidney or brain)

Diagnosing Thrombosis and Thrombophilia

Some of our patients have already been diagnosed with a clot and need expert care.

We also see children and teens who have:

  • Symptoms of a clot
  • A family history of clots
  • Had a lab test that shows a problem with the genes that affect clotting (like factor V Leiden)

In all cases, 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 help judge the likelihood of a clot or how new or “active” a clot might be

  • 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:

    • Special ultrasound that uses sound waves to create pictures of 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 vessels blood flow (venogram)

  • Doctors will look for and treat the underlying cause of your child’s clot. Common causes include:

    • Problems with a central line
    • Lack of activity
    • A disease like irritable bowel disease or lupus
    • Use of birth control containing estrogen
    • A genetic disorder that increases clotting
    • Infection

    An inherited condition may cause your child to have frequent blood clots, clots in unusual locations or a stroke. Our doctors will work with your family to decide if genetic testing for thrombophilia is needed. We consider whether the results would change how we treat your child and whether other family members have been diagnosed with thrombophilia.

Treating Thrombosis and Thrombophilia

Some children with blood clotting problems only need treatment for a short time. Other children may need lifelong treatment. Treatment depends on what is causing the clot, how severe the clot is and whether this 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. We will work with your child’s other doctors to coordinate care.

Our 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:

  • Whether your child’s condition 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 reduce the blood’s ability to clot. These medicines also stop existing blood clots from getting bigger. However, they do not break up blood clots that have already formed. These medicines are also called anticoagulants (AN-te-ko-AG-u-lants).

    It is important to get the right amount so your child’s blood is not too thin. We tell you warning signs of thin blood and regularly check how well your child’s blood is clotting. Once levels are stable, most kids are tested every 2 to 4 weeks. We check more often for babies who are growing quickly and less often for teens who are stable.

    For families who don’t live in the Seattle area, our specially trained pharmacists help you find the closest lab for follow-up blood testing.

    These blood thinners are the most common:

    • Enoxaparin (Lovenox®). Your child gets this medicine as an injection under the skin.
    • Warfarin (Coumadin®), given in pill form. Before starting an oral medicine, doctors would give your child enoxaparin or heparin for at least 5 days. This is called “bridging.”
    • Heparin, through an IV tube. 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.
    We treat most new clots with enoxaparin. Children who need treatment for more than 3 months usually switch to medicine in pill form, such as warfarin.

    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.

    Novel oral anticoagulants (NOACs) are newer types of anticoagulants for adults that are not regularly used in children. Seattle Children’s is studying 1 of these medicines in children. Your doctor will talk with you about the study if it may be appropriate for your child.

  • Many blood clots dissolve on their own as time goes by. 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 do 1 or more of these:

    • Use medicines to quickly dissolve it. These are called thrombolytic agents. Doctors give them through a tube into your child’s vein (IV). The doctor uses imaging (such as a CT scan or ultrasound) to guide tube placement. We usually use thrombolytics only in life-threatening cases because of an increased risk of bleeding.
    • Use a mechanical “Roto-Rooter” device to break up the clot and suck it out. The device is attached to a tube inserted into the blood vessel, using imaging guidance.
    • Stretch the blood vessel to make it wider (angioplasty) using a tube placed in the blood vessel. There are different ways to do this, such as inflating a balloon attached to the tube or using a mesh tube (stent) that expands.

  • We take steps to reduce the chance of another blood clot from underlying causes 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. We offer these services:

    • Check your child’s risk for a clot, based on things like illness, infection, upcoming surgery and medicines they take.
    • Advise about getting tested for changes in genes (genetic testing).
    • Suggest 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.
    • Talk about options for birth control that don’t contain estrogen, which increases the risk of clots.
    • Give you information about thrombophilia and ways to prevent clots.
    Rarely, clot prevention includes taking medicines that interfere with the formation of blood clots (thrombin inhibitors). These medicines are only used for children in special situations, usually in the Intensive Care Unit. Our patients may be able to take part in a research study that is testing whether a thrombin inhibitor for adults is safe and effective for children.

Contact Us

Contact the Cancer and Blood Disorders Center at 206-987-2106 for an appointment, a second opinion or more information.

To make an appointment, you can call us directly or get a referral from your child’s primary care provider. We encourage you to coordinate with your pediatrician or family doctor when coming to Seattle Children’s.

Providers, see how to refer a patient.