Too much faith in imaging technology

Simple risk assessment tools are being overlooked in favour of CT pulmonary angiography

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Simple risk assessment tools are being overlooked in favour of CT pulmonary angiography in patients with suspected pulmonary embolism, exposing them to unnecessary harms, an Australian expert told the Preventing Overdiagnosis Conference in Barcelona earlier this month.

“There’s too much emphasis and faith placed in technology,” said Associate Professor Ian Scott, chief investigator at University of Queensland’s research centre into primary and secondary care integration.

“I think we resort to technology in the hope it will give us a definitive answer and allay our concerns that we might be

missing something, but in the process, what we’re doing is overdiagnosing the condition.”

More than half of all patients undergoing CTPA for suspected pulmonary embolism are receiving them unnecessarily, according to his research at the Princess Alexandra Hospital in Brisbane, which has been submitted for publication.

Beyond the potential radiation from the scan, or allergy to the dye contrast, unnecessary CTPA exposed patients to the risk of being diagnosed with an “incidentaloma”, Professor Scott said.

“It starts a cascade of investigation and treatment for things that were picked up incidentally on the CT scan, which may be completely benign and don’t cause the patient any concern over their lifetime,” said the director of the Department of Internal Medicine and Medical Assessment and Planning Unit at the hospital.

And thanks to technological improvements, CTPA could now identify very small clots in very small blood vessels, he said.

“But we don’t know what the natural history of those very small clots are,” he told TMR. “We suspect that they’re totally inconsequential.”

While the CTPA diagnosis of pulmonary embolus increased threefold over the last 20 years, mortality rates from the condition remained largely unchanged.

“If you do autopsy studies on people who die of completely unrelated conditions, often you can find very small clots in blood vessels of the lungs,” he said.

While diagnosing and treating major clots in larger vessels was of benefit, the evidence was not in to suggest a benefit from treating smaller clots.

“When people detect these very small clots, we tend to anticoagulate them on the basis that this may be something that could be potentially serious. But then we incur the risks of bleeding from the anticoagulation, which itself can be quite serious.”

Instead of jumping straight to CTPA, patients could be stratified into high and low-risk groups by using a common risk assessment score such as the modified Wells Score, along with a D-dimer assay, the research found.

Patients in the low risk category – which make up more than half the presentations to the emergency department – and a negative D-dimer assay have a “very, very low probability” of pulmonary embolism, Professor Scott said.

“The risk of missing one of these patients is less than 1%,” he said.

Instead, more confidence in  clinical acumen was needed.