Applied Evidence

Evaluation of the Patient with Suspected Deep Vein Thrombosis

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References

Pain and swelling of a leg is a relatively common presenting complaint in primary care practice. In the 1995 National Ambulatory Medical Care Survey, 1.3% of patients presenting to family physicians had a complaint of leg pain or swelling.1 Although this complaint often has a benign cause, it is important to carefully evaluate these patients because they may have deep vein thrombosis (DVT). A population-based study showed that 48 of 100,000 persons are given the diagnosis of DVT every year, which corresponds to 1 to 2 patients per year in a typical family physician’s panel of patients.2

Patients with a clotting abnormality who are pregnant, undergo a period of immobilization, or are diagnosed with a malignancy are at higher than average risk of DVT. In addition to the morbidity associated with DVT, approximately 40% of patients with DVT have a pulmonary embolism (PE), although most of these are clinically silent, and it is not clear whether aggressive work-up to diagnose PE in patients with DVT is indicated.3

This article describes an approach to the evaluation of patients with suspected DVT. The focus will be on making the best possible use of the history and physical examination by using our knowledge of the probability of DVT and validated clinical decision rules. This information will guide the interpretation of diagnostic tests such as d-dimer and duplex venous ultrasound.1

Differential diagnosis

There are many causes of leg pain and edema, including musculoskeletal injury, congestive heart failure, hepatic disease, mechanical obstruction of lymphatic drainage, cellulitis, malnutrition, thyroid disease, Baker cysts, chronic venous insufficiency, and venous thrombosis. Unfortunately, no detailed data are available for the percentage of patients given these diagnoses among all patients presenting with leg pain and swelling. Among all patients with leg pain with and without swelling only 3.3% had thrombophlebitis in a large Dutch series.4

A number of studies reporting data on the percentage of patients with suspected DVT who are referred for diagnostic testing and have the diagnosis confirmed are summarized in Table 1. As a rule of thumb, for every 100 outpatients with suspected DVT 16 will have a proximal DVT and 4 will have a distal DVT.

Using the history and physical examination

Individual signs and symptoms are of relatively little value in the diagnosis of DVT. The well-designed studies5,6 generally find a lower sensitivity or specificity for physical examination findings than poorly designed studies.7 The accuracy of individual history and examination findings are outlined in Table 2 using only data from the highest-quality study. Homan sign (long taught as a useful clinical sign) is of no value in the diagnosis of DVT and should be omitted from the examination.

However, groups of signs and symptoms can be useful. Wells and colleagues developed a clinical rule that combines the results of 9 carefully defined signs and symptoms Figure 1. They subsequently validated this rule in a later study using a different group of patients and found it useful for stratifying patients into separate groups by risk of having a DVT.8-10 This validation study included outpatients referred for the evaluation of suspected DVT to a tertiary care hospital thrombosis clinic. Patients were excluded if they were pregnant, had a lower extremity amputation, were suspected of having a PE, had symptoms for more than 60 days, or were currently using anticoagulants. The mean age was 57.1 years; 40% were men; and 16% were given a diagnosis of DVT. Thus, these data would generalize to a family practice setting. Patients who fell into the low-risk group based on this rule had a 3% risk of DVT; those in the moderate risk group, 17%; and those in the high-risk group, 75%. This information will determine how we interpret the results of the noninvasive tests.

Diagnostic tests

Tests for the diagnosis of DVT include impedance plethysmography, magnetic resonance imaging (MRI), duplex venous ultrasound, and contrast venography. The latter is an invasive test, typically considered the reference standard. The accuracy of noninvasive tests varies with the study population (symptomatic vs asymptomatic) and the type of DVT being diagnosed (proximal, distal, or any). The tests are generally much less accurate in asymptomatic patients and less accurate for distal DVTs. The data for impedance plethysmography and ultrasound are summarized in Table 3 for symptomatic patients.11-13 Although duplex venous ultrasound is clearly the preferred test, impedance plethysmography is an acceptable alternative if ultrasound is not available.

Although there is considerable interest in MRI, studies to date have been small14-16 or have had serious methodologic limitations, such as a failure to blind the radiologists, a retrospective design, or a poor quality reference standard.17-19 In these studies, the sensitivity ranges from 80% to 100% and the specificity from 93% to 100% when compared with contrast venography. Consideration of MRI should currently be limited to cases where venography is considered but there are concerns over the use of contrast, and where there is considerable local experience with the technique.20,21

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