Authors' reply to Quantrill, Benger, Ripley and colleagues, Roach, Rogers, and Haldar and colleagues.

Quantrill’s concern underscores the tension between doing too much versus too little.1 2 Substantial evidence shows, however, that selective imaging based on diagnostic algorithms is not only safe,3 4 but preferable, because it reduces overtesting and overtreatment. Even Anderson and colleagues’ study, where all patients had a moderate to high pretest probability of pulmonary embolism, showed no difference between computed tomography (CT) pulmonary angiography and V/Q scanning in primary or secondary outcomes. The primary outcome was venous thromboembolism at 90 days and the secondary outcome was fatal pulmonary embolism or unexplained sudden death. The 0.6% difference in venous thromboembolism rates cited by Quantrill was deemed clinically and statistically insignificant.

We thank Benger for pointing out the PERC criteria,5 which like the Wells and Geneva scores, provide another evidence based approach for clinicians to minimise imaging of low risk patients.

We agree with Ripley and colleagues that excessive radiation exposure is an important harm of overuse of CT,6 and we thank Benger and Roach for highlighting alternative first line tests for venous thromboembolism.5 7 Although three dimensional V/Q SPECT seems to have advantages over the planar scans used in the US, it will be important to confirm that this new technology improves outcomes and does not compound the problem of overdiagnosis of clinically insignificant pulmonary embolism because of its high sensitivity.

Both Rogers and Haldar and colleagues highlight the role of the radiologist in the overdiagnosis of pulmonary embolism.8 9 Implementing systems of multiple readings may help reduce “overcalling” artefacts. Feeding back re-readings to radiologists may help calibrate them and improve inter-rater reliability. Regardless, radiology reports like those described by Haldar and colleagues that directly help clinicians understand the meaning of ambiguous findings (such as isolated subsegmental pulmonary embolism), their clinical importance, and possible treatment actions (or inaction) are a welcome step forward.