How are blood clots treated?

Explore how blood clots are treated.


Treatment of blood clots depends upon a number of factors, including the location of the clot and your health.

Generally, treatment is designed to:

  • prevent the existing blood clot from getting any larger
  • prevent a clot from breaking off and traveling to the lungs or other organs
  • prevent complications, such as post-thrombotic syndrome (leg pain and swelling)
  • prevent a blood clot from occurring again



Anticoagulants (Blood thinners)

The most common treatment is the use of blood thinning medication, known as anticoagulants. These medications decrease the blood's ability to clot, which helps prevent an existing blood clot from growing larger and also helps prevent the formation of new clots. They do not break up an existing blood clot. There are three main forms of anticoagulant you may encounter during treatment: heparin, low molecular weight heparin (LMWH), and warfarin (brand name = Coumadin®).



Heparin is an intravenous anticoagulant which is often given in the hospital immediately after the diagnosis of a blood clot.


Low molecular weight heparin (LMWH)

Low molecular weight heparin is a derivative of heparin which can be given by an injection just under the skin, either once or twice a day. Periodic blood tests are usually not needed to monitor the effectiveness of LMWH. LMWH goes by several brand names. While they differ a little pharmacologically, clinically they are all more or less equally effective and safe.

In the US the following LMWHs are available:

• Lovenox (= Enoxaparin)
• Fragmin (= Dalteparin)
• Innohep® (= Tinzaparin)

Outside the US the following LMWHs are also available:
• Fraxiparin ® (= Nadroparin)
• Clivarine ® (= Reviparin)
• Monoembolex ® (= Certoparin)


Warfarin (brand name = Coumadin®)

Warfarin (=coumadin® ) is an oral anticoagulant (pill) which prevents your blood from clotting too easily. It does that by preventing some of the clotting factors in the liver from being formed. Some people use the expression that warfarin (=coumadin® ) "thins" the blood, but, technically speaking, that term is not correct: blood of patients on warfarin (=coumadin® ) is of normal thickness (= viscosity). It just takes longer to clot. However, as a figure of speech the term "coumadin thins the blood" is often used.

Everybody needs a different dose of coumadin and there is little that predicts how much a person will need. It is therefore necessary to monitor the effect of coumadin so that the patient is not over- or underdosed. Otherwise, bleeding or re-clotting may occur.


The PT (= prothrombin time; "protime") measures, how “thin” the blood is. It measures how many seconds the patient’s blood plasma takes in the test tube to clot, after the plasma has been activated by an added lab reagent. The thinner the blood, the longer it takes to clot, and the longer is the PT. Because the clotting time also depends on the strength of the lab reagent used, a value is calculated from the PT that takes the strength of the reagent into consideration. The result is a value called INR (= International Normalized Ratio). This value is standardized, making it comparable from one lab to the other: a value of 2.5 in one lab equals a value of 2.5 in another lab. The PT expressed in seconds is not standardized, meaning that one gets discrepant results between different labs, and should therefore not be used to monitor warfarin (=coumadin®) therapy. The same is true for the so-called “PT ratio”, which is used by some physicians and patients.

Interpreting the INR:
• A person not on warfarin (=coumadin® ) has a value around 1.0 (usually between 0.7 - 1.3). This is called a "normal INR".
• Once a patient is on coumadin , the INR increases. The higher the INR, the "thinner" the blood. Patients with DVT or PE are often kept at a target INR range of 2.0 - 3.0. This is also called "therapeutic INR range". If the INR is above 3.0 in that patient, the blood is too "thin"; if the INR is below 2.0, the blood is not "thin" enough.
• If a patient has had a second clot in spite of a therapeutic INR, the physician may increase the target INR range to 2.5 - 3.5 or even to 3.0 - 3.5. If one gets above 3.5, there is usually no increased benefit regarding the protection from blood clots, but the risk of bleeding increases significantly.
• Some patients who have a lupus anticoagulant that influences the INR, rendering the INR unreliable. Warfarin (=coumadin® ) therapy in these patients needs to be monitored by a test different to the INR, such as factor II level, chromogenic factor X level, or the P&P test


Other therapies

"Clot busting" (thrombolytic) therapy

In some cases, 'clot busting' medication (thrombolytics: tPA, streptokinase, urokinase) may be used which works to rapidly dissolve blood clots, rather than simply preventing new clot formation. These medications are given intravenously in the hospital. These 'clot busting' medications increase the risk for serious bleeding and are therefore typically used only in life-threatening situations.


Vein filter

When the risk of a blood clot breaking off and traveling to the lungs is high, a vein filter (vena cava filter, Greenfield filter) can be inserted into the large vein in the abdomen (called the the inferior vena cava or IVC) which leads from the leg and pelvis area up to the heart. With the filter in place, a clot which breaks loose from a DVT (deep vein thrombosis) in the leg, gets caught in the filter and cannot then travel on to the lung, thus preventing a pulmonary embolism.



Compression stockings

Compression stockings are special hose which prevent swelling associated with DVT (deep vein thrombosis). To find stockings that fit well, these should be custom fitted with a patient's legs measured. They need to have a certain compression pressure, 35 mm Hg (mercury) at the ankle, 25 mm Hg at the mid-calf, and 18 mm Hg just below the knee (so-called grade 2 stockings). Stockings come in many different shapes, sizes, colors, materials, from many different companies.  Also, if there is leg swelling, elevation of the leg above the level of the heart while resting or sleeping is appropriate. Normalization of weight may also improve the symptoms quite significantly, as may regular exercise.


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