Simple ultrasound test shows promise for detecting blood clots in leg

16 October 2008

A comparison of two diagnostic methods used to detect deep vein thrombosis (DVT; a blood clot in a deep vein in the leg or thigh) of the lower extremities indicates that a simpler method, with wider availability, has rates of DVT detection that are equivalent to a more complex method, according to a study in the October 8 issue of JAMA (JAMA. 2008;300[14]:1653-1659).

The imaging technique, compression ultrasonography, is a highly accurate method for the detection of DVT and has replaced other diagnostic methods in common practice.

Two ultrasonography diagnostic methods often used are 2-point and whole-leg. With 2-point ultrasonography, compression is applied to two veins, and benefits include simplicity, reproducibility and broad availability (may be performed with virtually all ultrasound scanners, irrespective of age or model).

“Its major limitation is the need to repeat the test once within 1 week in patients with normal findings at presentation to detect calf DVT extending to the proximal [near the point of origin] veins. Repeat testing may be safely avoided in patients with a normal D-dimer test [blood test used to help rule out active blood clot formation] at presentation,” the authors write.

The advantages of whole-leg ultrasonography include the ability to exclude isolated calf DVT, allowing for 1-day treatment of all patients, without additional testing. Conversely, it needs top-quality ultrasound equipment and experienced operators; therefore, it is often unobtainable after hours and during the weekends.

Despite the lack of definite evidence, whole-leg ultrasonography is thought to be better than serial 2-point ultrasonography, and as a consequence, many patients with suspected DVT need to wait hours or even days before whole-leg ultrasonography is obtained and are frequently (unnecessarily) administered anticoagulants in the meantime, according to background information in the article.

Dr Enrico Bernardi, of the Civic Hospital, Conegliano, Italy, and colleagues conducted a study to determine if the two diagnostic strategies are equivalent for the treatment of patients with suspected DVT of the lower extremities. The randomized, multicenter study included 2,098 outpatients with a first episode of suspected DVT of the lower extremities who were randomized to undergo 2-point (n = 1,045) or whole-leg (n = 1,053) ultrasonography.

Of patients in the 2-point strategy group, the incidence of confirmed symptomatic venous thromboembolism (VTE; blood clots in the deep veins of the legs or in the lungs) during the 3-month follow-up period was 0.9 percent (7 of 801 patients). Of patients randomized to the whole-leg ultrasonography method, the incidence of confirmed symptomatic VTE during the follow-up period was 1.2 percent (9 of 763 patients).

“The observed difference between the 2 groups in terms of symptomatic VTE at the end of the 3-month follow-up period was 0.3 percent, which is within the chosen equivalence limit” the authors write. “Either strategy may be chosen based on the clinical context, on the patients’ needs, and on the available resources. [Two-point ultrasonography plus D-dimer] is simple, convenient, and widely available but requires repeat testing in one-fourth of the patients. [Whole-leg ultrasonography] offers a 1-day answer, desirable for patients with severe calf complaints, for travelers, and for those living far from the diagnostic service, but is cumbersome, possibly more expensive, and may expose patients to the risk of (unnecessary) anticoagulation.”

In an accompanying editorial (JAMA. 2008;300[14]:1696-1697), C Seth Landefeld, MD, of the University of California, San Francisco, San Francisco Veterans Affairs Medical Center, and Stanford University, Stanford, Calif., comments on the findings of Bernardi and colleagues.

“How should clinicians approach patients with a possible first episode of DVT? Based on the available evidence, it would be reasonable to choose 2 tests initially—a clinical prediction rule and D-dimer test, a clinical prediction rule and 2-point ultrasonography, or 2-point ultrasonography and a D-dimer test. If both tests are negative, DVT is effectively ruled out and anticoagulation can be withheld safely.”

“If DVT is not ruled out, 2-point ultrasonography should be performed if not already performed. If DVT has neither been ruled out nor diagnosed by ultrasound, a second ultrasound should be performed 1 week later; if that ultrasound is negative for DVT, no further testing is indicated. The results of the trial by Bernardi et al show that whole-leg ultrasonography has little advantage, unless a course of anticoagulant therapy for isolated calf DVT is preferable to repeating 2-point ultrasonography a week later.”

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