Question 4: What is the role of the computed tomography (CT) pulmonary angiogram of the chest as the sole diagnostic test in the exclusion of pulmonary embolism?

• Level A recommendations. None specified.
• Level B recommendations. For patients with a low or pulmonary embolism unlikely (Wells score 4 or less) pretest probability for pulmonary embolism who require additional diagnostic testing (e.g., positive D-dimer result or highly sensitive D-dimer test not available), a negative, multidetector CT pulmonary angiogram alone can be used to exclude pulmonary embolism.
• Level C recommendations. (1) For patients with an intermediate pretest probability for pulmonary embolism and a negative CT pulmonary angiogram result in whom a clinical concern for pulmonary embolism still exists and CT venography has not already been performed, consider additional diagnostic testing (e.g., D-dimer, lower-extremity imaging, ventilation perfusion [VQ] scanning, traditional pulmonary arteriography) prior to exclusion of VTE disease. (2) For patients with a high pretest probability for pulmonary embolism and a negative CT angiogram result, and CT venography has not already been performed, perform additional diagnostic testing (e.g., D-dimer, lower-extremity imaging, VQ scanning, traditional pulmonary arteriography) prior to exclusion of VTE disease.

Note that a negative, highly sensitive, quantitative D-dimer result in combination with a negative multidetector CT pulmonary angiogram result theoretically provides a posttest probability of venous thromboembolism disease less than 1%.

Spiral CT pulmonary angiography, when available, has replaced VQ lung scanning as the principal imaging modality for diagnosing PE in patients without contraindications (e.g., renal insufficiency, contrast allergy). With the technology advancing so rapidly, evidence regarding performance of the newest generation of CT scanners is lacking. Although diagnostic studies report sensitivity in the range of 90% for detection of pulmonary embolism, outcome studies suggest that non-high-risk patients with a negative CT angiogram have very low rates of VTE on 3-month follow-up. The addition of venous imaging either by concurrent CT venogram or by venous ultrasound of the lower extremities results in an incremental increase in sensitivity for detection of VTE disease. Also, high-risk patients with a negative D-dimer and negative CT angiogram have an extremely low rate of VTE on 3-month follow-up. As the reported false-negative rate of CT pulmonary angiogram alone in high-risk patients ranges from 5% to 40%, it is recommended that high-risk patients with a negative CT angiogram undergo additional diagnostic testing prior to ruling out VTE.

Although there has been an explosion of research in PE and in VTE disease, there are still many unanswered questions.

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