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Determining the duration of anticoagulant treatment for VTE

For how long will I need to take anticoagulants?
Recommendations on treatment length?
Unknown causes: is treatment different for PE than for DVT?
What about the risk of bleeding?
How do we know when it is safe to stop treatment?
Reference

For how long will I need to take anticoagulants?
“I have just been diagnosed with a venous blood clot, but I am otherwise healthy. For how long will I need to take anticoagulants? How long will it take for the clot to resolve?” The answers may vary from patient to patient. If you have been promptly diagnosed and treated appropriately with anticoagulants, your symptoms will generally improve very quickly – sometimes within hours to a few days; residual swelling of the leg and discomfort related to a deep vein thrombosis (DVT) or chest pain from a pulmonary embolus (PE) may persist a bit longer, but at most for up to 10 days. The underlying blood clot – either a DVT or PE – will still be present, however. For this reason, you will need to take anticoagulant therapy for a longer time, usually for at least 3 months.

Even 3 months may not be long enough. A study of DVT patients who stopped taking oral anticoagulant therapy after 3 months found that as many as 1 in 10 had another blood clot within the next year.

Recommendations on treatment length
Your physician will make a decision on the length of treatment based on your symptoms and medical history, and taking into account current recommendations from professional organizations. For example, in 2004, the American College of Chest Physicians issued advice on the duration of anticoagulant therapy, defining 5 different types of patient with DVT – their recommendations are summarized by the INATE Advisory Group as follows:

• Patients with their first DVT who have a known temporary risk factor (or factors). Such factors include use of an oral contraceptive, pregnancy, surgery (eg orthopedic surgery), trauma/injury, and immobilization (eg while in a cast after a fracture, or after long-haul air travel). If you are in this category of patient, 3 months of treatment with oral anticoagulants is likely to be enough, as you have a very low risk of the clot recurring. If you are pregnant, you will probably be prescribed low-molecular-weight heparin (LMWH, another type of anticoagulant), to be taken for 3 to 6 months and until 6 weeks after giving birth.
• Patients with their first DVT who also have cancer. If you are in this category, you will need to take LMWH for the first 3 to 6 months, and then long-term oral anticoagulant therapy – this will need to be taken indefinitely unless the cancer is cured. (For more on links between cancer and blood clots, see this article.)
• Patients with their first DVT, which is of unknown cause (idiopathic). If you are in this category, you will require an extended course of oral anticoagulants, lasting 6 to 12 months. Your physician may decide that you need treatment for a longer period, and perhaps indefinitely, as there is evidence in this group of patients that the benefits of treatment do not persist after treatment is stopped – clots may be more likely to recur than in other types of patient.
• Patients with their first DVT who also possess factors favoring the formation or recurrence of a clot. There are many such factors, which your physician will test for. They include the factor V Leiden mutation and antiphospholipid antibody syndrome (APS). If you have one such factor, you are likely to require oral anticoagulant therapy for at least 6 to 12 months (your physician may also decide that you need indefinite treatment). If you have two or more factors, or if you just have APS, your physician is likely to prescribe at least 12 months of oral anticoagulant therapy (and possibly indefinite treatment).
• Patients with recurrent DVT, eg patients who have had at least one DVT before. If this applies to you, your physician may recommend indefinite treatment with an oral anticoagulant.

Please note that these are recommendations only; your physician may prescribe a different length of treatment, after taking into account individual factors such as your medical history and response to treatment.

Unknown causes: is treatment different for PE than for DVT?
Another common question is whether patients with PE of unknown cause (so-called idiopathic PE) should be treated differently than patients with idiopathic DVT. It is potentially more dangerous for a patient to develop a recurrent PE than a recurrent DVT. For this reason, physicians may be more likely to prescribe long-term treatment (eg for at least 6 to 12 months) for idiopathic PE than for idiopathic DVT.

If you have idiopathic PE, your physician may perform a range of tests before deciding that you no longer require anticoagulant therapy. These tests, depending on availability, may include a spiral CT scan of your chest to make sure that your clots have dissolved; a fibrin D-dimer test to check that your blood clotting system is not “activated” or that the clot is no longer present or likely to recur, and an echocardiogram to rule out heart problems due to recurrent PE.

What about the risk of bleeding?
Anticoagulant therapy acts on components of the blood to prevent a new clot from forming. However, a side effect of this action is an increased risk of bleeding. Several factors have been shown to affect this risk, including age, and the dosage and duration of anticoagulant therapy. Your physician will consider your individual risk of bleeding when determining the length of treatment that you require.

A standard way for physicians to minimize bleeding risks during oral anticoagulation therapy (with drugs like Warfarin, that antagonize vitamin K) is to perform regular blood tests to ensure that you are receiving the correct amount of anticoagulant drug. Your physician does this by checking your International Normalized Ratio (INR), a measure of the time it takes your blood to clot in a test tube. Insuring that your INR remains at the recommended level (between 2 and 3) will help minimize the risk of bleeding.

How do we know when it is safe to stop treatment?
How is it determined whether or not it is safe to stop treatment with anticoagulants? Usually you will have some tests to confirm that the clot has been dissolved. However, the range of tests available to a physician may vary from location to location. In addition, there is little evidence from studies to support any particular schedule of tests over any other.

For this reason, it is not possible to state exactly which tests you may undergo. However, you can get an idea from the approach described by a specialist in an article in the Professionals section of INATE.org. This specialist’s approach is to first obtain a scan to find out whether or not the clot is still present (radionucleotide perfusion lung scanning, or contrast computerized tomography, for PE; compression ultrasound for DVT).

Based on the results, the specialist discusses with the patient whether or not to continue anticoagulant therapy. If treatment is continued, another scan is performed after 3 months. If there is no improvement and the patient has been treated with oral anticoagulants, the patient may be switched to treatment with LMWH by injections for an additional 3 months with a repeat scan at the end of this period to determine whether or not this treatment should be stopped or continued.

Reference
Buller HR, Agnelli G, Hull RD, et al. Antithrombotic therapy for venous thromboembolic disease: the Seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy. Chest. 2004;126:401S-428S.