Clots in the lung

Figure. Suggested serial diagnostic testing strategy for patients presenting to the ED with varying clinical pretest probabilities of pulmonary embolism (PE). a, Conservative assessment of evidence supports use of VIDAS DD D -dimer assay in this setting. b, Negative (–) VIDAS DD D -dimer assay in low clinical pretest probability patients essentially excludes PE (<1% posttest probability). c, Evidence supporting use of negative VIDAS DD D -dimer result in intermediate clinical pretest probability patients for exclusion of PE appears valid; however, because the precision of the LR ^– cannot be estimated, this test cannot be recommended at this time as unequivocally safe among intermediate clinical probability patients. d, Negative VIDAS DD D -dimer result does not exclude PE among high clinical pretest probability patients. e, A/C denotes anticoagulation for treatment of venous thromboembolic disease. f, Patients with underlying cardiopulmonary disease, especially chronic lung disease, may bypass radionuclide lung scanning and proceed directly to sCTA. g, See text for indications for ventilation scanning after a perfusion study. h, Negative lung scan finding indicates a reading of normal or near-normal. i, (±) finding on lung scan indicates a clinically indeterminate reading (ie, neither normal/near-normal nor high-probability [very low, low, intermediate, and so forth]). j, Positive (+) lung scan indicates a high probability reading. k, sCTA denotes spiral (helical) CT angiography with contrast, not requiring catheterization. l, A plausible alternative diagnosis seen on sCTA is currently the only evidence-based means of excluding PE with this test. m, Angio denotes conventional pulmonary angiography, requiring catheterization.