Diagnostic Strategies for Deep Vein Thrombosis
The approach to the diagnosis of deep vein thrombosis varies because of differences in local resources and expertise. A number of strategies are acceptable depending upon the availability of resources and expertise. The goal of any diagnostic strategy is to diagnose deep vein thrombosis accurately so that patients with deep vein thrombosis receive appropriate treatment and patients without deep vein thrombosis avoid the risks of prolonged anticoagulation.
Symptomatic Outpatients with Suspected Deep Vein Thrombosis
Calf vein thrombi rarely cause pulmonary embolism unless the thrombi extend into more proximal deep veins. Furthermore, untreated calf vein thrombi propagate into proximal deep veins in approximately 25% of patients,  and noninvasive techniques are less sensitive for the detection of isolated calf vein thrombi.[4,36] These key concepts anchor diagnostic strategies for patients with symptoms that suggest deep vein thrombosis.
Clinical outcome studies have demonstrated the safety of withholding anticoagulants when serial noninvasive tests (either IPG or compression ultra-sonography) are negative.[36,37,38,61] At present, compression ultrasonography with a single repeated examination 5 to 7 days later is appropriate for evaluation of most symptomatic outpatients with suspected lower extremity deep vein thrombosis. The technique is simple -- only the common femoral and popliteal veins are assessed for compressibility -- and clinical outcome studies have shown that less than 2% of patients experience thromboembolic events during a 3-month follow-up period when anticoagulants are withheld on the basis of negative results.[37,38] Clinical scoring of pretest probability,  D-dimer tests,  or comprehensive compression ultra-sonography examinations may eventually eliminate the need for a repeated examination, but these approaches require more investigation.
Occasionally, clinical circumstances dictate a more aggressive diagnostic approach. Compression ultrasonography is not sensitive for the detection of isolated iliac vein thrombi,  and failure to identify such thrombi may prove fatal. Some patients are unable to return for a repeated compression ultra-sonography examination, and some patients may have technically inadequate compression ultra-sonography. In these circumstances, and when clinical suspicion of deep vein thrombosis is high, alternative approaches such as contrast venography or magnetic resonance imaging are appropriate.[7,11]
Similarly, a more aggressive diagnostic approach is necessary when clinical suspicion is low or when circumstances favor a falsely positive compression ultrasonography examination. Noncompressibility limited to the common femoral vein in patients with extensive pelvic disease (e.g., neoplasms or radiation) often does not represent venous thrombosis. In this circumstance, venography or magnetic resonance imaging is appropriate to confirm or exclude the diagnosis.
Symptoms and Signs that Suggest Upper Extremity Deep Vein Thrombosis
Compression ultrasonography is both sensitive and specific for the detection of upper extremity deep vein thrombosis,[63,64] and these attributes make compression ultrasonography the preferred initial test when the physician suspects axillary-subclavian vein thrombosis. As with lower extremity thrombosis, when the pretest clinical suspicion differs from the results of compression ultrasonography, additional testing is necessary. Either contrast venography or magnetic resonance imaging is useful in such cases.
Pregnant Patients with Symptoms that Suggest Deep Vein Thrombosis
During pregnancy, deep vein thrombosis often occurs in the deep veins of the left calf or iliac vein.[65,66] Noninvasive techniques such as IPG and compression ultrasonography may not detect these thrombi. For this reason, a combined approach to the diagnosis of deep vein thrombosis is needed. Compression ultrasonography is the first test, but if compression ultrasonography is negative, then magnetic resonance imaging or contrast venography should be employed, particularly when isolated iliac vein thrombosis is suspected (whole leg edema). The risk posed to the fetus by radiation exposure with contrast venography is acceptable.[3,67]
Patients with Prior Deep Vein Thrombosis and Symptoms or Signs that Suggest Recurrent Acute Deep Vein Thrombosis
The diagnosis of recurrent deep vein thrombosis is difficult. Repeated contrast venography remains the reference standard, but few patients have under-gone venography at the time of initial diagnosis. Impedance plethysmography can confirm recurrent deep vein thrombosis when the original episode has resolved sufficiently to yield a normal IPG and a sub-sequent IPG is abnormal in the setting of a clinically suspected recurrence. Compression ultrasonography is not suited to the kinds of precise comparison that repeat contrast venography permits. However, it is often necessary to repeat the compression ultra-sonography examination for evidence of involvement in a new venous segment, in order to diagnose symtomatic recurrent deep vein thrombosis.
Asymptomatic High-Risk Postoperative Patients
Neither compression ultrasonography nor impedance plethysmography is sensitive for the detection of deep vein thrombosis in asymptomatic patients at high risk for deep vein thrombosis.[18,21,22,23,24,25,26,27,28,29,30] These techniques fail to detect both proximal and calf thrombi in this situation, and routine surveillance of high-risk patients is not recommended. One randomized clinical trial examined the role of predischarge compression ultrasonography after hip or knee arthroplasty. The investigators found that routine screening compression ultrasonography did not affect patient outcomes. Contrast venography remains the only reliable screening test for such patients, but its use has been restricted to clinical trials because of risk and cost.
Patients with Symptoms and Signs that Suggest Acute Pulmonary Embolism
Both compression ultrasonography and IPG have a role in the evaluation of patients with symptoms and signs that suggest acute pulmonary embolism. Noninvasive tests of the lower extremities are helpful when ventilation and perfusion lung scans are not diagnostic. The detection of proximal vein thrombi allows treatment to proceed without pulmonary arteriography, and serial negative leg studies allow anticoagulants to be withheld safely when patients have good cardiopulmonary reserve ( Table 12 ).[70,71] Unfortunately, only a small fraction of patients with nondiagnostic lung scans have deep vein thrombi detectable by compression ultrasonography. Conversely, a substantial number of patients with nondiagnostic lung scans and serial negative compression ultrasonography or IPG studies can be managed safely without anticoagulants.[71,73] Hull et al reported that only 1.9% of 586 patients had objectively proven venous thromboembolism during a 3-month follow-up period; when anticoagulants were withheld after serial negative IPG examinations over a 14-day period. Wells et al reported that only 3 of 665 (0.5%) patients with low or moderate clinical suspicion of acute pulmonary embolism, non-high probability ventilation-perfusion lung scans, and serial compression ultrasonography had new pulmonary embolism during a 3-month follow-up period without anticoagulants.
Semin Respir Crit Care Med. 2000;21(6) © 2000 Thieme Medical Publishers
Cite this: The Diagnostic Approach to Deep Venous Thrombosis - Medscape - Dec 01, 2000.