In light of increased use of CT for the evaluation of patients with suspected pulmonary embolism despite a lack of evidence that this has improved outcomes, the American College of Physicians (ACP) has released a new paper arguing that patients should be stratified into groups based on more appropriate diagnostic strategies.

Instead of routine CT, physicians should use a validated clinical prediction rule, such as the Wells and Geneva rules, to estimate a patient’s probability of pulmonary embolism, according to the paper published Sep. 29 in Annals of Internal Medicine.

Imaging should be avoided as an initial test for patients with a low or intermediate pre-test probability of pulmonary embolism, wrote Ali S. Raja, MD, Vice Chair of the Department of Emergency Medicine at Massachusetts General Hospital, and colleagues who authored the paper for ACP's Clinical Guidelines Committee.

For patients with a low pre-test probability, the Pulmonary Embolism Rule-Out Criteria (PERC) rule should then be used to further weigh the risks of testing against the risk of pulmonary embolism. D-dimer blood testing could provide additional risk stratification, but should be avoided in those with a low probability of pulmonary embolism who meet all eight criteria of PERC.

"While highly sensitive, plasma D-dimer testing is nonspecific and false-positives can lead to unnecessary imaging," said Raja in a statement.

For those with an intermediate pre-test probability of pulmonary embolism or those with a low probability who do not meet all PERC criteria, a D-dimer test should be the initial step in diagnosis.

ACP urges the use of age-adjusted D-dimer thresholds to determine whether imaging is warranted, as D-dimer levels increase with age. Rather than the generic threshold of 500 ng/mL, Raja and colleagues advised multiplying patient age by 10 ng/mL in patients older than 50 years to get a new threshold.

"The use of an age-adjusted threshold resulted in maintenance of sensitivities with improved specificities in all age groups,” said Raja.

CT pulmonary angiography should be performed in patients with a high pre-test probability of pulmonary embolism, while ventilation/perfusion lung scans should be reserved for when CT pulmonary angiography is contraindicated or not available, according to the ACP guidelines.