Reliability and Safety of Managing Patients with Suspected Blood Clots in the Legs Using Comprehensive Duplex Ultrasonography

Summaries for Patients are a service provided by Annals to help patients better understand the complicated and often mystifying language of modern medicine.

Summaries for Patients are presented for informational purposes only. These summaries are not a substitute for advice from your own medical provider. If you have questions about this material, or need medical advice about your own health or situation, please contact your physician. The summaries may be reproduced for not-for-profit educational purposes only. Any other uses must be approved by the American College of Physicians.

The summary below is from the full report titled "Withholding Anticoagulation after a Negative Result on Duplex Ultrasonography for Suspected Symptomatic Deep Venous Thrombosis." It is in the 15 June 2004 issue of Annals of Internal Medicine (volume 140, pages 985-991). The authors are S.M. Stevens, C.G. Elliott, K.J. Chan, M.J. Egger, and K.M. Ahmed.

What is the problem and what is known about it so far?

Serious illness or death can occur if blood clots (thrombi) form in the deep veins of the legs (a situation known as deep venous thrombosis or DVT) and then become dislodged and flow with the bloodstream to the lungs. Thrombi that reach the lungs are called pulmonary emboli. Deep venous thrombosis and pulmonary emboli are treated with blood thinners (anticoagulants). Unfortunately, anticoagulants themselves can cause side effects (such as bleeding) that may be fatal, so they must be used carefully and only in confirmed cases of DVT. Confirmation can be obtained by using one of several available ultrasonography methods that use sound waves to detect the presence of thrombi. The most commonly used method is called simplified compression ultrasonography. While this test reliably identifies (or rules out) thrombi above the knee, it cannot detect thrombi in the calf veins (below the knee). A significant clinical problem is that once thrombi form in the calf veins, they sometimes extend upward above the knee before dislodging and causing pulmonary emboli. For this reason, patients with negative results on simplified compression ultrasonography must be retested a week later to detect thrombi that were missed on the first test. Not only is repetition of the test expensive and inconvenient, it is frequently unnecessary because 80% of retested patients have no evidence of thrombi. Another test, called comprehensive duplex ultrasonography, is more time-consuming and difficult to perform but can effectively detect thrombi in the calf vein and the upper leg and may not require retesting when the initial results are negative.

Why did the researchers do this particular study?

To determine the safety of withholding anticoagulants from patients who were suspected of having DVT and had a negative result on a single examination with comprehensive duplex ultrasonography.

Who was studied?

445 consecutive patients with a suspected first episode of DVT.

What did the researchers do?

Comprehensive duplex ultrasonography was performed from groin to ankle in all study participants. When the test results were negative, no anticoagulant was given, even if symptoms or physical examination findings suggested that thrombi were present. Patients were advised to return for reevaluation if their symptoms changed. All patients were interviewed 3 months later to see if they had any evidence of DVT or pulmonary emboli.

What did the researchers find?

Three hundred seventy-five patients had negative results on comprehensive duplex ultrasonography, remained in the study, and received no anticoagulants. Twenty-two of these 375 had symptoms over the next 3 months, but further testing showed that only 3 had DVT. Six patients died, none of pulmonary emboli.

What are the limitations of the study?

Pregnant women and others who did not fit characteristics of the study group were excluded, so the results cannot be applied to all situations where DVT is suspected.

What are the implications of the study?

Patients with a suspected first episode of DVT can be managed safely without anticoagulants if a single comprehensive duplex ultrasonogram is negative, eliminating the need for repeated testing.