Expanded Testing for Pulmonary Embolism Leads CT Scan Overuse

Looking further at how our emergency medicine experts view the evaluation for PE, Jeff Kline offers a comprehensive summary of risk factors and diagnostic considerations.^8,9 In his view, nonspecific cardiopulmonary symptoms are not sufficient in isolation to reasonably consider the possibility of PE. Patients must have physiologic manifestations of PE absent an alternative cause, paired with the presence of at least one known risk factor for PE. Risk-stratification into low, intermediate, or high risk can be performed by gestalt, Wells score, or revised Geneva score. Low-risk patients who meet the PE rule-out criteria fulfill an unfavorable risk-to-benefit ratio, and testing should be avoided. For otherwise low- and intermediate-risk patients, quantitative D-dimer testing is recommended.

Better yet, Kline has also proposed dynamically adjusting the D-dimer cutoff level based on the pretest probability.¹⁰ In a review of 126 patients diagnosed with PE, there were 11 patients for whom the pretest likelihood of PE was low and who had D-dimer levels less than 1000 ng/mL. All but one was subsegmental, representing less than 5 percent of the pulmonary vascular tree, and none had concomitant deep venous thrombosis. Accounting for the risks of anticoagulation, the increasing prevalence of false-positive CT pulmonary arteriography, and the risks of contrast-induced nephropathy, it may yet prove reasonable to forgo CT in this subset of patients. However, until better evidence becomes available, such a strategy should be approached via shared decision making, balancing the risks of small, undiagnosed PE against those associated with anticoagulation.

As vessel size decreases, the quality of opacification and contrast capture diminishes. This results in consistent ambiguity regarding the presence of a flow-limiting lesion.

There is no question that widespread use of CT has provided substantial benefit to patients and the health care system. However, its ubiquity and ease of use is leading to unintended consequences, particularly in overdiagnosis paired with substantial risks of unnecessary treatment. Every effort should be made to reduce use of CT in those with low pretest likelihood of PE, and small, subsegmental PE should be viewed with suspicion in the context of individual patient factors. We must continue to refine and reflect upon our routine evaluation of cardiopulmonary complaints, lest our pursuit of this white whale slip into madness.

Dr. Radecki is assistant professor of emergency medicine at The University of Texas Medical School at Houston. He blogs at Emergency Medicine Literature of Note and can be found on Twitter @emlitofnote.