KidsMD Health Topics

Thrombosis (Blood Clots)

  • When they help prevent bleeding, blood clots are a normal and healthy function of the human body. However, a thrombosis (or thrombus) is an excessive or dangerous blood clot that develops somewhere it shouldn’t.

    Thrombophilia refers to a group of disorders that increases a child’s tendency to develop excessive and dangerous blood clots, which can block blood supply to and damage organs and tissues. Thrombosis in children is uncommon, and is most often seen in children with complex medical problems.

    The disorder can be thought of as the opposite of hemophilia, which prevents the blood from clotting.

    How Dana-Farber/Boston Children's approaches blood clots

    Children with abnormal blood clots are treated through our Thrombosis and Anticoagulation Program. At Dana-Farber/Boston Children's Cancer and Blood Disorders Center, we offer advanced treatment options for children with thrombosis and thrombophilia.

    • The team’s established monitoring and risk identification guidelines quickly identify children who need anticoagulation medications (or “blood-thinners”).
    • Children may receive anticoagulation therapy to reduce the risk of developing a clot or to treat a clot.
    • Children outside of the hospital visit our outpatient center staffed by pediatric hematologists and pediatric hematology nurse practitioners very familiar with the diagnosis and treatment of thrombosis.
    • Alan Michelson, MD, director of the Thrombosis and Anticoagulation Program, is an expert in the field of platelets and platelet disorders. He is the editor of Platelets, the field’s premier academic journal on these conditions.
    • Dana-Farber/Boston Children's Cancer and Blood Disorders Center is home to the Center for Platelet Research Studies (, an active research program in thrombosis and anticoagulation.
  • What is a blood clot?

    If your child skins his knee or scrapes his elbow, a complex series of reactions in his bloodstream initiate the formation of a blood clot, which stops the bleeding. Blood clots are a normal and healthy function of the human body that prevent blood loss in the event of injury. However, if a clot blocks the inside of a blood vessel (thrombosis), serious tissue injury can result.

    • A thrombosis may lead to loss of blood supply and severe tissue damage.
    • Left untreated, a thrombosis can cause long-term problems, such as permanent damage to the internal organs.


    What are the causes of thrombosis?

    One common cause of developing a pediatric thrombosis is thrombophilia, a group of disorders that increases a child’s tendency to develop excessive or dangerous blood clots in places where they shouldn’t, like the calf or lung. Thrombophilia can be thought of as the opposite of hemophilia, a disorder that prevents the blood from clotting.

    There are two kinds of thrombophilia:

    Inherited thrombophilia, caused by certain genetic conditions, including:

    • Factor V Leiden
    • Prothrombin gene mutation
    • Protein C, protein S or antithrombin deficiencies

    Acquired thrombophilia, caused by lifestyle factors or medical conditions, including:

    • immobility
    • obesity
    • sedentary lifestyle
    • trauma

    In teens and adults, risk factors also may include:

    • smoking
    • oral contraceptive use

    Where does a thrombosis usually develop in children?

    A thrombosis may occur anywhere in the child’s body, but most are in the calf (deep vein thrombosis, DVT) or lungs (called a pulmonary embolus). Other types of thrombosis include sinus venous thrombosis (cerebral vein clots) and arterial thrombosis.


    What are the symptoms of a thrombosis?

    The symptoms of blood clots in children can vary significantly depending on its size and location, and each child may experience symptoms differently.

    If your child has a thrombosis in the calf, he or she may experience symptoms, such as:

    • swelling
    • pain
    • redness and warmth
    • low-grade fever

    In some cases, you may even be able to feel the clot in the back of your child’s calf like a knot under the skin.

    If your child has a pulmonary embolus, or thrombosis that has traveled to the lungs, he or she may experience chest pain or shortness of breath.

    A pulmonary embolus is a medical emergency, and you should seek immediate medical attention if you suspect your child has a pulmonary embolus.

    The symptoms of blood clots in children may resemble those of other diseases. Always consult your child’s physician for a diagnosis.

    If my child has a blood clot, is he more likely to have another?

    Some children are genetically predisposed to developing blood clots, a condition known as thrombophilia. Your child’s physician will determine whether the clot was caused by a type of thrombophilia or occurred for a different reason.

    What are the possible complications of blood clots?

    Clots can block the flow of blood, cutting off the supply of oxygen to parts of the body. Without oxygen, cells start to die, which can cause severe, permanent damage to internal organs and other body tissues. The degree of complications depends largely on the location and size of the clot.

    Based on the size and location of the clot, your child’s physician will recommend a specific course of treatment to minimize complications.

  • Our doctors will conduct a physical examination to evaluate symptoms of a blood clot. The thrombosis will be confirmed through imaging tests, such as:

    We may collect blood samples to evaluate whether your child’s blood is clotting normally and identify any abnormalities in the levels of certain proteins. Genetic tests also may be performed to check for hereditary disorders (inherited thrombophilia).

    After we complete all necessary tests, our experts meet to review and discuss what they have learned about your child's condition. Then we will meet with you and your family to discuss the results and outline the best treatment options.

  • Children treated for a pediatric thrombosis through Dana-Farber/Boston Children's Cancer and Blood Disorders Center's Thrombosis and Anticoagulation Program are often seen as inpatients. Outpatient treatment and follow-up care are provided through our hematology clinic. For certain appointments and procedures, your child may also receive care at one of our satellite offices.

    Your child’s treatment team will determine a specific care plan based on several factors, but it’s likely that she will receive anticoagulation medications (“blood thinners”). These medications prevent the clot from growing, decrease the risk of its breaking apart and causing further complications and help heal the blood vessel. Your child may need to continue taking these medications for several months after initial treatment.

    Examples of anticoagulation medication your child’s physician may prescribe include:

    • oral agents such as warfarin (Coumadin)
    • intravenous heparin
    • injections under the skin (also called subcutaneous injections) of a low molecular weight heparin such as enoxaparin (Lovenox) or dalteparin (Fragmin)
    • antiplatelet agents such as aspirin, clopidogrel (Plavix) or prasugrel (Effient)

    Other treatments may include wearing compression stockings, remaining active and applying heat to reduce the swelling and pain caused by the clot.

    Coping and support

    We have a number of resources at Dana-Farber/Boston Children’s to help you and your family through this time.

    Patient education: From the first visit through follow-up care, our nurses will be on hand to walk you through your child’s treatment and help answer any questions you may have. They also will reach out to you by phone, continuing the care and support you received while at Dana-Farber/Boston Children’s.

    Parent to parent: Want to talk with someone whose child has been treated for thrombosis? We can often put you in touch with other families who have been through the same experience that you and your child are facing, and can share their experience.

    Faith-based support: If you are in need of spiritual support, we will help connect you with the chaplaincy at Boston Children's Hospital. Our program includes nearly a dozen clergy representing Episcopal, Jewish, Lutheran, Muslim, Roman Catholic, Unitarian and United Church of Christ traditions who will listen to you, pray with you and help you observe your own faith practices during your hospital experience.

    Social work and mental health professionals: Our social workers and mental health clinicians have helped many other families in your situation. We can offer counseling and assistance with issues such as coping with your child’s diagnosis, stresses relating to coping with illness and dealing with financial difficulties.

    On our For Patients and Families site, you can read all you need to know about:

  • Children with thrombosis are treated through the Dana-Farber/Boston Children's Thrombosis and Anticoagulation ProgramAlan Michelson, MD, our program’s director, is an expert in the field of platelets and platelet disorders. He is the editor of Platelets, the field’s premier academic journal on these conditions. He also directs the Center for Platelet Research Studies, an internationally recognized, multi-disciplinary research center in thrombosis and anticoagulation.

    The center’s researchers perform scientific and clinical research on platelets and related aspects of hemostasis and thrombosis. A particular focus is antiplatelet therapy, including the characterization of:

    • how newly discovered molecules and mechanisms could help control platelets and clotting
    • how antiplatelet drugs affect normal blood clotting (coagulation) and aspects of the immune system (e.g., inflammation)
    • the relationship between the strength of antiplatelet treatments and the balance between thrombosis (uncontrolled clotting) and hemorrhage (uncontrolled bleeding)
    • how tests of platelet function could help guide antiplatelet therapy in the clinic
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