Lower extremity deep vein thrombosis: Diagnosis

History and physical examination help to identify the possibility of deep vein thrombosis before performing investigations. The diagnosis is confirmed by Doppler ultrasonography with flow study (duplex ultrasonography). The need for additional studies (eg, D-dimer study), their choice and sequence depend on the results of the ultrasound. No existing protocol of the study is recognized as the best.

Ultrasound detects thrombi by directly visualizing the venous wall and demonstrates abnormal compression properties of the vein, while Doppler ultrasonography demonstrates impaired venous flow. The study has a sensitivity of more than 90% and a specificity of more than 95% for thrombosis of the femoral and popliteal veins, but is less accurate for iliac or calf vein thrombosis.

If the pretest probability of deep vein thrombosis is moderate to high, D-dimer should be measured simultaneously with duplex ultrasonography. D-dimer is a byproduct of fibrinolysis, and elevated levels suggest recent thrombus formation and dissociation. The test has a sensitivity of over 90% but a specificity of only 5%; thus, elevated levels are not diagnostic, but the absence of circulating D-dimer helps exclude deep vein thrombosis, particularly when the initial assessment of deep vein thrombosis probability is < 50% and duplex ultrasonography is negative. There have been cases of negative D-dimer (using enzyme-linked immunosorbent assay) in the presence of deep vein thrombosis and pulmonary embolism. However, newer latex agglutination or whole blood agglutination methods (more definitive and rapid methods) will likely allow D-dimer testing to be used routinely to exclude deep vein thrombosis when the likelihood is low to moderate.

Contrast venography is rarely used because the radiopaque agent can cause venous thrombosis and allergic reactions, and ultrasonography is atraumatic, more accessible, and can detect deep vein thrombosis with almost the same accuracy. Venography is used when ultrasound results are normal, but preliminary studies indicate deep vein thrombosis, or when ultrasound reveals pathology and suspicion of deep vein thrombosis is low. The complication rate is 2%, mainly due to allergic reactions to the contrast.

Noninvasive alternatives to contrast venography are under study. These include magnetic resonance venography and targeted MRI of thrombi using specialized techniques such as T1-weighted echo imaging; the latter could theoretically provide simultaneous visualization of thrombi in the deep veins and subsegmental pulmonary arteries.

Patients with confirmed deep vein thrombosis and an obvious cause (eg, immobilization, surgery, leg trauma) do not require any further testing. If symptoms raise suspicion of pulmonary embolism, additional testing (eg, ventilation-perfusion scanning or helical CT) is used.

Tests for hypercoagulability are controversial but are sometimes indicated in patients with idiopathic recurrent deep vein thrombosis, in those with deep vein thrombosis and a personal or family history of other thromboses, and in younger patients without obvious predisposing factors. Some evidence suggests that the presence of a hypercoagulable state does not predict recurrent deep vein thrombosis, nor do clinical risk factors. Screening of patients with deep vein thrombosis for malignancy has low success rates. Routine screening with a complete history and physical examination aimed at detecting malignancy and specific diagnostic tests ordered based on the results of the test is more appropriate.

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