Beth Waldron, Clot Connect program director, writes…
If you’ve experienced deep vein thrombosis (DVT) or pulmonary embolism (PE), a recurrence of a blood clot in the future is a concern. Diagnosing a recurrent clot can be a challenge because it is sometimes difficult to tell if symptoms are the result of a new clot or the signs of chronic damage from the initial clot.
- Around 40% of patients with DVT develop long-term pain and swelling, known as post-thrombotic syndrome. Such pain and swelling can fluctuate, and be particularly pronounced after standing for prolonged periods of time or being overly active.
- Around 4% of patients with PE develop long-term shortness of breath, known as pulmonary hypertension.
How do healthcare professionals know when symptoms are the result of a past blood clot or due to a new clot?
Your physician uses clinical guidelines and guidance statements developed by professional medical societies to determine the most up-to-date recommendations and clinical evidence related to the prevention, diagnosis and treatment of blood clots. There are currently over fifteen professional guidelines and guidance statements covering a wide range of diagnosis and treatment issues related to deep vein thrombosis (DVT) and pulmonary embolism (PE).
New guidance on the diagnosis of recurrent DVT and PE has recently been issued by the Scientific and Standardization Committee (SSC) of the International Society on Thrombosis and Haemostasis (ISTH). (Ref 1)
Here is the diagnostic approach suggested by this guidance for patients suspected of having a DVT or PE recurrence:
1. Pre-test probability assessment
Symptoms of DVT and PE can mimic other common, non-serious conditions. Physicians often utilize assessment tools (scored checklists) to determine if a patient who presents with leg or breathing symptoms is at low, moderate or high risk of having suffered a DVT or PE. These risk assessment scores help the physician determine which patient should get blood labs (D-dimer test) or imaging studies(ultrasound or lung scans).Use of these risk assessment tools avoids unnecessary tests and provides more optimal care for the patient and better utilization of health care resources. One such assessment tool is called the Wells score and you can view it here. (Ref 2). It is referred to as a ‘pre-test probability assessment’ because it occurs before any other diagnostic tests are done.
2. D-dimer blood test
If the initial pre-test probability assessment shows that a patient has a LOW probability of having a clot, it is suggested that patients should get a D-dimer blood test.
- D-dimer is a protein found in blood which is a breakdown product of blood clots. It is often increased in people with clots.
If you are determined to have a low-risk for DVT (based upon the history and physical examination) and the D-dimer test is negative, further testing with an imaging study to rule out a blood clot is not needed. However, if the D-dimer is positive, this does not prove that a clot is present. A number of other things can lead to increased D-dimer levels (trauma, recent surgery, liver disease, etc.). A positive Dimer needs to be followed up with an imaging study.
3. Doppler ultrasound
If the initial pre-test probability assessment shows that a patient has a MODERATE or HIGH probability of having a DVT, it is suggested the patient should not get a D-dimer blood test, but go straight to getting a venous Doppler ultrasound.
- Doppler ultrasound (Duplex) is a painless and noninvasive test used to diagnose DVT. During a Doppler ultrasound, sound waves are used to generate pictures of the blood vessels.
It is sometimes difficult to tell if the results of a Doppler ultrasound are the result of new clot or old clot. In that situation, it is suggested that further evaluation be done: D-dimer testing and possibly other imaging studies (such as CT-venogram, MR-venogram).
4. CT pulmonary angiogram (CTPA)
If the initial pre-test probability assessment shows that a patient has a MODERATE or HIGH probability of having a PE, it is suggested the patient should not get a D-dimer blood test, but go straight to getting an imaging study called a computed tomography pulmonary angiogram (CTPA).
- You may hear CTPA referred to more simply as a “CT scan” or “CTA”. It uses a combination of x-rays taken from many different angles to produce detailed pictures of inside the body. An intravenous injection of contrast dye is given to make blood vessels more visible.
Additional recommendations which may aide diagnosis:
It is suggested that, when a patient with DVT stops anticoagulant (blood thinning) therapy, a Doppler ultrasound of the leg should be obtained. This provides a baseline study which can be used for comparison should future leg symptoms arise. It may aide in determining if what is seen on an ultrasound may be due to new clot and what may be the result of chronic, residual changes (= scar tissue) from a previous clot.
However, for patients with PE, a follow-up scan (CTPA) is not recommended when discontinuing anticoagulant (blood thinning) therapy. While a baseline can aide in ruling out recurrence, it comes with both concerns about the health effects of the additional radiation exposure and cost considerations. A baseline scan may be considered, however, in patients felt to have a high risk of recurrence.
Note: the above guidance does not apply to patients with clots in unusual locations (such as clots in the abdomen or around the brain). For these patients, little data exists to guide diagnosing recurrent events.
- Ageno W et al. The diagnosis of symptomatic recurrent pulmonary embolism and deep vein thrombosis: guidance from the SSC of the ISTH. Accepted Article. J Thromb Haemost, May 18,2013, http://onlinelibrary.wiley.com/doi/10.1111/jth.12301/abstract .
- Wells PS et al. Does this patient have deep vein thrombosis? JAMA 2006;295:199-207.