Fears of missing a pulmonary thromboembolism in patients who present to emergency departments could be driving an overuse of CT pulmonary angiography to rule out the condition – exposing many patients to unnecessary risks associated with the scans, a leading physician has warned.
Speaking to the limbic Dr Ian Scott, Director of the Department of internal medicine and clinical epidemiology at Princess Alexandra Hospital in Brisbane said many doctors are bypassing risk assessments like the modified Wells score and D-dimer in favour of the highly sensitive test first-line when a pulmonary thromboembolism (PE) is suspected.
But as more clinicians turn to highly sensitive imaging without first assessing risk, more patients are being treated for small clots that show up on imaging that will not have gone on to have any clinical significance.
“Unfortunately our healthcare system has got all sorts of perverse incentives – people put in an incentive to deal with one problem and it creates another problem down the track,” Dr Scott said.
For example, a pressure to meet the “four-hour rule” in emergency departments may result in clinicians choosing to opt for a scan rather than wait up to an hour for a D-dimer assay.
“CT pulmonary angiography (CTPA) is at the moment too readily used – its so easily accessible available 24/7. The problem is that people feel like this is the gold standard because it takes a lot of the uncertainly out of a doctor’s mind as to whether the patient has a PE or not.”
But Dr Scott argued that there are many trade-offs that come with relying too heavily on the technology.
“In quite a number of CTPAs you’ll find a very small sub segmental clot which may be an artefact, people are not entirely sure whether they are true clots or not, but unfortunately people don’t reconcile that very small abnormality with the patient’s symptoms, which usually don’t really correlate at all.”
He said in a lot of cases many doctors might feel ‘compelled’ to start patients on anticoagulants because they think they might have a PE.
“That entails the risk of bleeding as the result of that unnecessary anticoagulant…we’re seeing a lot of that now,” he said.
He argued that overuse of the test could be curtailed by more consistent use of the modified Wells score, coupled with D-dimer assays in patients who have low risk scores.
“If you’ve got a low risk patient with a Wells score of less than 4 and you have a negative D-dimer then your risk is getting down to less than 5% … in such patients, even if it was PE it’s likely to be small, it’s not going to be a big clot sitting in the main pulmonary artery or even in the lobar arteries.
“It’s likely to be a small PE somewhere out in the sub segmental arteries – patients are not going to die from those, that’s not something you need to actively treat there and then” he said.
The effects of radiation exposure sustained while undergoing CTPA should also not be overlooked.
“There are some offsetting features in relation to the radiation and admittedly that’s not a lot but in a young female you really should think twice about giving CTPA – its equal to at least 20 x-rays,” he pointed out.
A recent study headed up by Dr Scott suggested that more than half of requests for CTPA in patients with suspected PE may not be justified, with this figure rising to almost three quarters in low risk patients.