Management: Clotting

Risk of Blood Clotting in Patients with K-T and Vascular Malformations

References: Oduber et al 2013, Gonsalves et al 2013 (Mayo Clinic Proceedings), Conners 2015 (NEJM)
Most people with K-T and similar combined vascular malformation conditions will have an increased risk of abnormal blood clotting at some point in their life. This increased risk is not typically associated with inherited abnormalities in blood clotting factors. Current theories suggest the clotting may be due to flaws in the internal structure of the veins which causes a buildup of fibrin and platelets, or due to the abnormal structure of the venous malformations.

Clots can develop in any area of the body, regardless of which part of the body is affected by K-T or the VM, although studies have shown that the more extensive the VMs the greater the risk of clotting. 

Abnormal clotting can occur as early as young childhood or infancy. In most cases however things such as trauma, surgery, hormonal changes (such as with puberty or pregnancy), aging, and some medications (such as estrogen containing birth control or menopausal treatment) will lead to increased clotting risk.

There are two primary types of blood clots that can occur in K-T and VM patients:

  • Superficial clots: These will usually show up as a swollen blur, purple or red lump on the skin. There may or may not be bruising surrounding it. These can be painful, but they are not usually dangerous and will typically go away after several weeks on their own.
  • Deep venous clots: These are far more dangerous. There may or may not be pain or other warning symptoms. Any symptoms suspicious of a DVT or PE needs to be immediately checked out in an emergency room. Waiting could be life threatening.
    • Deep venous thrombosis (DVT) These clots occur in a deep vein, usually in a limb, blocking primary circulation in the affected limb. Symptoms may include cramping, swelling, or abnormal heat and redness in the affected limb. If not treated quickly, these clots can break off and cause more risk to the patient.
    • Pulmonary embolism (PE): When a clot occurring in a different part of the body breaks off and travels to the lungs, it is called a pulmonary embolism. Symptoms can include chest pain, difficulty breathing, a feeling of pressure on the chest, a drop in oxygen levels, and chronic coughing. In some rare cases death can occur with little to no warning.
    • Rarely a deep venous blood clot in a patient with combined vascular malformation may lead to a stroke, or a sudden interruption in the blood supply of the brain.

3D illustration of a clot


Blood clots in the leg or arm are usually detected with ultrasound. However, venogram, which uses a combination of x-ray and flourescent dye injected into the vein, is still occassionally used.
Pulmonary emboli or PE (clots which travelled to the lungs) are typically detected with a CT scan, although occasionally a PET scan or MRI may be ordered. An X-ray of the lungs will not be able to detect a PE.

Key blood lab warnings of a possible DVT or PE include: 

  • elevated d-dimer
  • prolonged prothrombin time
  • changes in blood fibrin or fibrinogen levels

Other labs such as lower protein C, lower free protein S, and higher plasmin-antiplasmin (PAP) complexes can also be red flags.


Prevention of thrombosis in combined vascular malformations, or reduction of risk, can involve proactive measures such as using compression, avoiding steroidal hormone treatments such as estrogen therapy, not smoking, ensuring enough activity to reduce blood pooling without causing excess pain and stress, elevation of the affected limb(s), and avoiding circumstances of trauma to the area when possible.

  • In some cases, a medical doctor may recommend aspirin or 81 grain aspirin therapy.
  • If planning pregnancy or going into surgery, it is important to discuss clotting risk with your doctor.

In someone with K-T and K-T like combined vascular malformation disorders, proactive measures may not be enough to prevent clotting. Once a diagnosis of coagulopathy (high blood clot potential or a history of clots) has been made, other measures may be needed to prevent or reduce the risk of a recurrence.

The use of anticoagulants (medicines that inhibit blood clotting through various methods) is usually started by a doctor after someone has had a recent blood clot episode so as to prevent future clots from happening. Below is a list of the types of anticoagulants or antiplatelets currently available. For a summary of the types of anticoagulants see Table 1.

Common NameGeneric NameOTC or RxDeliveryHow it WorksAntidote
AspirinAcetylsalicylic AcidOTCOralAntiplateletPlatelet  Transfusion
CoumadinWarfarinRxOralVitamin K  InhibitorVitamin K
PradaxaDabigratranRxOralInhibits thrombin (Factor IIa)Praxabind
XareltoRivaroxabanRxOralFactor Xa inhibitorIn trials
EliquisApixabanRxIV or  InjectionFactor IIa inhibitorIn trials
UF HeparinNARxIV or  InjectionFactor IIa and Xa inhibitorProtamine sullfate
LMW HeparinNARxIV or InjectionFactor Xa InhibitorProtamine (partially effective)

Types of anticoagulants currently available:

  • Acetylsalicylic acid (aspirin): Technically an anti-platelet medication. Although developed as an over-the-counter anti-inflammatory pain medicine, a few decades ago the medical field discovered that aspirin reduces clotting by blocking the clumping of platelets. Aspirin for reduced risk of clotting should only be taken with recommendation from a doctor. Low dose aspirin or adult aspirin may be recommended depending on the circumstances. If aspirin is not enough to reduce coagulation risk, then prescription anticoagulants or anti-platelets may be needed.
  • Prescription anti-platelets: These include Plavix, Effient and others. Like aspirin, they work by reducing platelet clumping. However one dose lasts longer compared to aspirin. Platelets don't normalize on their own, only when replaced by new bone marrow platelets when the medicine stops (this takes about 7 days).
  • Warfarin (Coumadin): This has been prescribed for several decades. Due to how the liver metabolizes warfarin, warfarin dose must be titrated individually which requires regular labs. It is very important to keep track of labs to make sure the blood doesn't become "too thin" (increased bleeding risk) or "too thick (increased clotting risk). Changes in diet, supplements, and medications can change how warfarin is metabolized and so should always be reported to the clinic with followup labs.
  • In the past few years, new prescription oral anticoagulants have been developed which work by blocking the action of "clotting factors". These "factors" are protein molecules your body makes that control how your blood clots. Although the human body makes many types of clotting factors, these medicines can reduce someone's risk by blocking just a single type. 
  • Unfractionated (UF) Heparin: This is not used very often due to risks, however it is an option in some cases. When provided it is administered by IV or injection.
  • Low Molecular Weight Heparin (LMWH): This is generally safer than unfractionated heparin. It is delivered by injection and can also be used safely during pregnancy.

IVC (Inferior Vena Cava Filters)

An IVC filter does not actually prevent clot formation. However, when anticoagulant therapy isn't enough to stop dangerous clots from forming, an IVC filter can be placed as a way of blocking clots from traveling. The filter, or mesh, is placed into the inferior vena cava. If clots form, break off, and travel, they are stopped by the mesh instead of traveling to the lungs or elsewhere. This protects the person from possible pulmonary embolism or stroke. Some filters can be replaced or removed, depending on the patient's clotting status and health needs.


At the time of diagnosis for a deep vein thrombosis, standard protocol usually involves hospitalization. The patient is monitored to ensure the clot does not break off and travel. In the hospital, a patient may also receive LMWH treatments by injections and/or have an IVC filter placed at the doctor's discretion. There may also be pain management if necessary. How long the hospitalization lasts will depend on the patient's status and doctor's medical judgement. Follow up afterwards usually involves a plan for anticoagulation.

For pulmonary embolism, hospitalization is also common, though not always the case. The patient's blood oxygen status, pain level, vitals, and blood clotting labs will be monitored. A patient may receive LMWH treatments by injections and /or have an IVC filter placed at the doctor's discretion. When considered safe, the patient will be released with a follow up plan for anticoagulation therapy.

Page last updated December 20, 2017