Patient Education Blog

Incidentally Discovered Blood Clots

General comments

CT scans and MRI scans are often done in medicine, for a variety of reasons.  Every so often such a scan will detect a blood clot in a patient who has no symptoms from the clot. This is referred to as an “incidental VTE”  (VTE = venous thromboembolism, i.e. clot in a vein) or “asymptomatic VTE”.  Such a clot may be a DVT in the pelvis or leg, in the major abdominal vein (vena cava), or in one of the intestinal veins (portal vein, splenic vein, mesenteric vein, or renal vein). When such an incidental, asymptomatic VTE is discovered, the question arises whether the patient should be treated with “blood thinners” or not. Very little is known about such incidental clots, few clinical studies exist. And due to the sparseness of data from clinical trials, no solid recommendations can be given.

How often are such incidental clots found?

One study found that one of 40 patients (2.6 %) who had a CT of the chest had an incidental PE [ref 1]. These are mostly patients who have some risk factors for DVT or PE, i.e. patients who are hospitalized or those with cancer.  Another study found that in cancer patients who undergo so-called staging CTS, i.e. extensive CTs to determine how extensive their cancer is, 2.5 % of patients (1 in 40) have a VTE; about half of these are leg or pelvic DVTs or PEs, the other half consists of clots in the abdomen (portal, mesenteric and renal vein clots) [ref 2].

Should patients with incidentally discovered clots be treated with “blood thinners”?

No studies have been performed to investigate whether such patients benefit from “blood thinners” or not.  Therefore, no clear recommendations can be given. Finding an asymptomatic DVT, particularly in the thigh or the pelvis, or a PE, many physicians will probably put the patient on blood thinners for some period of time (several months), unless the clot appears to be old by the way it looks on the CT or MRI scan.

What treatment guidelines exist?

The highly respected ACCP guidelines (American College of Chest Physician) recommends that patients with incidentally discovered asymptomatic DVT or PE should receive blood thinners just like patients who have a DVT or PE that cause symptoms [ref 4]. However, while this is a strong recommendation, it is based on low or very low-quality clinical trial evidence (so called Grade 1C recommendation). The guidelines do not take reference to how clots in the abdomen should be treated.

My personal approach

Decision making on “blood thinners” yes/no for incidentally discovered vein clots needs to take into consideration a patient’s risk factors for new clot (immobility, surgery, cancer, etc) and risk factors for bleeding. Then a very individualized decision needs to be made. If the patient has no significant risk factors for bleeding, I have a tendency to recommend “blood thinners” for a few months.

References

  1. Dentali F et al. Prevalence and clinical history of incidental, asymptomatic PE: A meta-analysis. Thromb Res 2010;125:518-522.
  2. Douma RA et al. Incidental VTE in cancer patients: prevalence and consequence. Thromb Res 2010;125:e306-e309.
  3. Dentali F et al. Prognostic relevance of asymptomatic venous thromboembolism in patients with cancer. J Thromb Haemost 2011;ePub.
  4. Kearon C et al. Antithrombotic therapy for venous thromboembolic disease. American College of  Chest Physician Evidence-Based Clinical Pratice Guidelines. Chest 2008;133:454S-545S.
For Health Care Professionals: This same information, written for health care professionals, is available here.

Disclosure: I have no financial conflict of interest with the content of this post.

Last updated: April 22nd, 2011

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