Treatment of venous thromboembolism

The prompt diagnosis and treatment of a blood clot is important. Deep vein thrombosis (DVT) and pulmonary embolism (PE) are treated with drugs called anticoagulants, which interact with clotting factors in the blood to inhibit the clotting cascade. Anticoagulants prevent a clot from getting larger and reduce the risk of other clots developing. For DVT, anticoagulants reduce the risk of an embolus travelling to the lungs and causing a PE. With anticoagulant treatment, existing clots usually eventually dissolve and disappear over time. Effective anticoagulation is important to reduce the long-term side effects of DVT and PE, particularly recurrence and the risk of post-thrombotic syndrome.


Anticoagulants (sometimes referred to as ‘blood thinners’) are the most common treatment for VTE. Three main types of anticoagulants are used to treat VTE: heparin, warfarin, and new oral anticoagulants (NOACs for short or DOACs (direct oral anticoagulants)). Treatment requires either one anticoagulant or two depending on the anticoagulants preferred by the clinic.

Most often, anticoagulation requires two drugs. Low-molecular-weight heparin injections and warfarin tablets are started at the same time. Warfarin takes a few days to become effective and adequately anticoagulate the blood. An International Normalised Ratio or ‘INR’ test is used to measure how well the anticoagulant drugs are working. During the initial treatment, heparin and warfarin are taken together until the INR is 2.5. When the INR reaches this level, the heparin injections are discontinued and the patient continues taking warfarin tablets depending on the patients history. The INR value must stay within the range of 2–3 during treatment, and is monitored by regular blood testing. The dose of warfarin is increased or decreased to ensure the correct range is maintained. This is important to reduce the risk of too much or too little anticoagulation.

Recently, doctors have started to prescribe new oral anticoagulants—often referred to as NOACs—that are different from heparin and warfarin. In the case of two of the NOAC anticoagulants, injections of heparin are not required; this may have advantages for patients who do not want to take injections. NOACs are given at a higher dose for several weeks at the start of treatment, followed by a reduced dose until the end of treatment.

As anticoagulants help stop blood clots from forming, it is important to be aware that they consequently increase the risk of bleeding and a wound may take longer to heal in the event of an injury.

In most cases, patients with DVT are treated as outpatients and hospital admission is not required. In some cases of uncomplicated PE, outpatient treatment is also possible. However, PE is a serious medical condition and often a patient is admitted to hospital to initiate the anticoagulant treatment.

The duration of anticoagulation depends on the circumstances that led to the development of the DVT or PE. If a patient has a temporary risk factor, for example recent immobility because of injury or illness, treatment may last 6 weeks to 6 months. If the risk factor is persistent, such as a thrombophilia, or the doctor believes there is an increased risk for recurrent clots, long-term anticoagulation as secondary prevention may be continued for years.

Compression stockings (also called graduated compression stockings) are often prescribed after a DVT. They can relieve pain, reduce swelling, and help to prevent long-term side effects of DVT such as post-thrombotic syndrome. These should be fitted professionally, and may need to be worn for 2 years or more.

Figure: compression stockings are often prescribed as part of the treatment of VTE

More on low-molecular-weight heparin

Heparins can be given intravenously (into a vein) or subcutaneously (under the skin) and specifically target blood clotting factors to prevent clot formation. Heparin starts to work immediately, which is why injections are given initially together with warfarin, which takes longer to start working. There are two different types of heparin injection that can be used to treat VTE: standard (unfractionated) heparin and low-molecular-weight heparin (LMWH).

Unfractionated heparin can work differently from person to person, and therefore the patient needs to stay in hospital during treatment to be monitored and have the dose adjusted if necessary. For this reason unfractionated heparin is rarely used nowadays. LMWH works slightly differently from unfractionated heparin. It contains smaller molecules, which means that its effects are more predictable. LMWH can be given as regular injections without the need to stay in hospital to be monitored.

Other treatments for VTE

Thrombolytics are drugs used in selected cases to dissolve blood clots, in particular in severe cases of PE. Thrombolytic treatment is used infrequently because it carries a high risk of bleeding as a side effect. Very occasionally, a surgical procedure called a thrombectomy is performed to remove the blood clot.