Study questions value of repeat CT exams after initial scan shows up negative for pulmonary embolism
Repeating CT pulmonary angiography (CTPA) imaging after an initial negative exam may have limited diagnostic value, according to new research published in Emergency Radiology.
When analyzing new data, researchers found substantially lower pulmonary embolism detection rates on repeat CTPA exams of patients who initially were flagged as having normal results. Experts suggest that their findings support the more selective use repeat CTPA scans, guided by a patient’s clinical pretest probability, which would help reduce unnecessary imaging and radiation exposure.
“CT pulmonary angiography is among the imaging tests most frequently identified as potentially overused. Pulmonary embolism is a common and potentially fatal condition with diverse clinical presentations, posing diagnostic challenges that may partly explain the high use of imaging for suspected PE,” Natalia Gorelik, with the department of diagnostic radiology at McGill University in Montreal, Quebec, and colleagues noted. “Despite increasing use of CTPA, there has been little change in mortality from PE.”
Researchers retrospectively evaluated adults who underwent CTPA across three emergency departments between 2016 and 2017. Patients with a negative initial CTPA were followed for two years to identify repeat examinations and compare their diagnostic yield with that of the index scan.
Among 3,112 patients included in the study, about 11% (or 331) had a positive initial CTPA. Of the 2,412 patients with a negative index exam, 12% (or 297) underwent another CTPA within two years. The diagnostic yield of repeat CTPAs performed in the emergency department declined as the interval from the initial examination increased. At one month, 1 of 26 repeat exams was positive, representing a 4% diagnostic yield. At one year, 9 of 150 examinations were positive, for a 6% yield; by two years, 13 of 202 repeat scans were positive, corresponding to a 6% yield.
Researchers noted that repeat imaging may still be appropriate when a patient’s clinical circumstances change or suspicion for pulmonary embolism remains high. However, the findings highlight the importance of reassessing clinical probability before automatically repeating CTPA after a negative examination.
With CTPA frequently used in emergency settings to evaluate suspected pulmonary embolism, the study suggests that incorporating clinical risk assessment into decisions about repeat imaging could help radiology and emergency medicine teams balance diagnostic benefit with unnecessary testing.
“Although repeat testing has been identified as a potential area of overuse by the Medicare Payment Advisory Commission, and a classification system for repeat imaging of the same anatomic site has been developed by the Harvey L. Neiman Health Policy Institute, there remains a paucity of studies evaluating the impact of prior negative imaging on subsequent workup for acute conditions,” the authors noted. “Addressing this gap could enable more precise quantification of individual risk, support optimal decision-making, and reduce unnecessary harms of CT imaging, particularly in light of the risks associated with cumulative radiation exposure.”
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In addition to her background in journalism, Hannah also has patient-facing experience in clinical settings, having spent more than 12 years working as a registered rad tech. She began covering the medical imaging industry for Innovate Healthcare in 2021.