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CTPA Scans in Low and Intermediate Probability Patients: Are We Choosing Wisely?

By: Ingrid Wirth, Raza Naqvi; Brent Burbridge and Erika Penz (supervisors)

CT pulmonary angiography (CTPA) scans are being used with increasing frequency to investigate for the presence of pulmonary embolism (PE). However, their potential risks along with the low rate of positive scans have led to the development of guidelines indicating the most appropriate use of this investigation. Both Thrombosis Canada and Choosing Wisely Canada recommend that patients with a low or intermediate pretest probability of PE first undergo d-dimer testing, and those with a negative d-dimer do not require a CTPA scan. The purpose of this study was to determine whether the use of CTPA scans in Saskatoon hospitals is consistent with the Choosing Wisely and Thrombosis Canada guidelines.

This retrospective review included 643 CTPA scans performed on non-pregnant adults in Saskatoon hospitals during January, April, July, and October, 2018. Pretest probability of PE was determined using both the Wells and PERC scores.

Only 48% of patients with a low or intermediate probability Wells score had a d-dimer tested prior to the CTPA scan, and 9% of those d-dimers were negative. 1% of the CTPA scans were performed on patients who had a negative PERC score.

None of the scans performed on low or intermediate probability patients with a negative d-dimer were conclusively positive for PE, whereas 25% of the scans performed on PERC-negative patients were positive.

The findings that fewer than half of low or intermediate probability patients had a d-dimer tested prior to receiving a CTPA scan, and that approximately 4% of scans in this study were performed inappropriately on low or intermediate probability patients with a known negative d-dimer, demonstrate that greater adherence to the Thrombosis Canada and Choosing Wisely Canada guidelines is warranted. A quality improvement initiative implementing a clinical decision support tool may promote more guideline-adherent use of CTPA scans in our health region.

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