American Thoracic Society Develops Guidelines on Diagnosis of Venous Thromboembolism

American Family Physician,  Feb 15, 2000  by Sharon Scott Morey

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The American Thoracic Society (ATS) has developed clinical practice guidelines for the diagnosis of acute venous thromboembolism. The guidelines were written by the ATS clinical practice committee and cover the diagnostic approach to acute deep venous thrombosis and to acute pulmonary embolism. The guidelines are published in the September 1999 issue of the American Journal of Respiratory and Critical Care Medicine. The document is available on the World Wide Web to subscribers of ATS journals online (http://www.atsjournals.org).

According to the ATS guidelines, venous thromboembolism is diagnosed in 260,000 patients each year, but data indicate that more than one half of the cases remain undiagnosed, which translates to an estimated annual incidence of 600,000 cases. The large number of missed cases of venous thromboembolism is one of the reasons the guidelines were formulated. The 15-member ATS clinical practice committee reviewed data from clinical trials that have evaluated the diagnostic approach to deep venous thrombosis and pulmonary embolism and categorized the data as Level 1 and Level 2. Level 1 data were from prospective studies of consecutively enrolled patients, used established objective diagnostic criteria for normal and abnormal results on diagnostic studies, and included independent comparisons of the diagnostic results with contrast venography for deep venous thrombosis and pulmonary angiography for pulmonary embolism (with interpreters of the tests blinded to other test results). Level 2 data were from all other clinical trials that did not meet the criteria for Level 1 studies.

The following highlights the two sections that summarize the diagnostic approach to deep venous thrombosis and to pulmonary embolism.

Diagnostic Approach to Deep Venous Thrombosis

The guidelines divide the diagnostic approach to deep venous thrombosis into symptomatic deep venous thrombosis of the lower extremity; asymptomatic deep venous thrombosis; recurrent, chronic deep venous thrombosis of the lower extremity; and upper extremity deep venous thrombosis. An algorithm for the diagnosis of acute deep venous thrombosis is on page 1196.

* Symptomatic deep venous thrombosis of the lower extremity. According to the guidelines, the initial diagnostic study for cases of suspected proximal deep venous thrombosis is compression ultrasound or impedance plethysmography. The decision regarding which study to perform depends on available resources.

The guidelines stipulate that positive findings on impedance plethysmography can be considered reliable as long as the clincal conditions associated with a high false-positive rate are recognized. If the results of impedance plethysmography are initially negative, the diagnostic approach should then be individualized according to the clinical situation.

Compression ultrasonography is described in the guidelines as highly sensitive and specific in symptomatic patients with acute proximal deep venous thrombosis. As long as compression is used, a clear advantage of one ultrasound technique over another (i.e., real-time B-mode imaging, duplex ultrasound and color Doppler) has not been demonstrated. The guidelines also state that studies support the use of serial ultrasound examinations, such as five to seven days after the initial evaluation, in patients with negative results on the initial study. According to the guidelines, serial impedance plethysmography and ultrasound are sensitive methods for detecting proximal extension of deep venous thrombosis of the calf in symptomatic patients.

The diagnostic efficacy of ultrasound may be reduced when the examination is abbreviated, such as when evaluation of the femoral vein is omitted. Studies suggest that a limited initial examination that includes the common femoral vein in the groin and the popliteal vein down to the trifurcation of the calf veins is sufficient. If the ultrasound findings are negative, a repeat study can be performed in one week. According to the guidelines, two negative studies five to seven days apart are associated with an acceptably low rate of thromboembolic complications as a result of withholding anticoagulation.

Contrast venography or magnetic resonance imaging (MRI) is the appropriate study if the diagnosis of deep venous thrombosis remains in question after ultrasound or impedance plethysmography.

While contrast venography is considered the most accurate diagnostic test for acute deep venous thrombosis of the calf, the guidelines state that ultrasonographic evidence of thrombosis can be relied on in symptomatic cases. Ultrasound is less reliable for pelvic vein thrombosis. Contrast venography, MRI and impedance plethysmography are considered sensitive for iliac vein thrombosis.

The guidelines note that general recommendations for the use of D-dimer assays cannot be made because of the lack of outcome data.

* Asymptomatic deep venous thrombosis of the lower extremity. The guidelines note that data indicate no proven utility in screening asymptomatic patients for deep venous thrombosis. The sensitivity of ultrasound is too low in asymptomatic high-risk patients for it to be considered a screening test.