Diagnosis of deep venous thrombosis and pulmonary embolism.

Venous thromboembolism manifests as deep venous thrombosis (DVT) or pulmonary embolism, and has a mortality rate of 6 to 12 percent. Well-validated clinical prediction rules are available to determine the pretest probability of DVT and pulmonary embolism. When the likelihood of DVT is low, a negative D-dimer assay result excludes DVT. Likewise, a low pretest probability with a negative D-dimer assay result excludes the diagnosis of pulmonary embolism. If the likelihood of DVT is intermediate to high, compression ultrasonography should be performed. Impedance plethysmography, contrast venography, and magnetic resonance venography are available to assess for DVT, but are not widely used. Pulmonary embolism is usually a consequence of DVT and is associated with greater mortality. Multidetector computed tomography angiography is the diagnostic test of choice when the technology is available and appropriate for the patient. It is warranted in patients who may have a pulmonary embolism and a positive D-dimer assay result, or in patients who have a high pretest probability of pulmonary embolism, regardless of D-dimer assay result. Ventilation-perfusion scanning is an acceptable alternative to computed tomography angiography in select settings. Pulmonary angiography is needed only when the clinical suspicion for pulmonary embolism remains high, even when less invasive study results are negative. In unstable emergent cases highly suspicious for pulmonary embolism, echocardiography may be used to evaluate for right ventricular dysfunction, which is indicative of but not diagnostic for pulmonary embolism.