lung tomographyThe diagnostic use of CT pulmonary angiography for pulmonary embolism is causing overdiagnosis of the condition, according to analysis published in BMJ. Using the imaging technology has been associated with an 80% rise in the detection of pulmonary emboli in the US, but with little change in death rates, according to researchers.
Using national U.S. data, the authors show an 80% rise in incidence of pulmonary embolism in the eight years after CT pulmonary angiography was introduced and a substantial increase in complications from anti-clotting treatment, as well as fear and anxiety for patients following diagnosis and treatment.
Despite this, deaths from pulmonary embolism in the U.S. changed little, while in-hospital deaths decreased by a third, suggesting that the extra emboli being detected are less lethal.
“If all pulmonary emboli caused important harm or death if untreated, finding more small clots would be an unqualified advance,” the authors noted. “However, there is evidence that some small clots do not need treatment, and finding them represents overdiagnosis. It has been argued that a normal function of the lungs is to act as a sieve to prevent small emboli formed in leg veins from travelling to the systemic arterial circulation with devastating effect, such as stroke. These emboli are believed to be resorbed by the body without treatment and to have no clinical effect.”
Investigators believe this idea is supported by the finding that “a surprisingly high proportion of consecutive contrast CT scans performed for other indications found incidental pulmonary emboli: in 16% of mechanically ventilated patients, in 17% of inpatients over age 80, and in 20% of trauma patients. In addition, 50-60% of consecutive patients having autopsy were found to have an unsuspected pulmonary embolism when the pulmonary arteries were carefully dissected.”
A related editorial gives several red flags for possible overdiagnosis, including incidence increase while mortality stays the same, labeling a risk factor or biomarker to sound like a disease, or a shift in diagnostic definitions or thresholds with no clear evidence that benefits are greater than harms.
The article is the first of a series looking at the risks and harms of overdiagnosis in a range of common conditions. The series, together with the planned Preventing Overdiagnosis Conference, are part of BMJ’s Too Much Medicine Campaign, which “aims to highlight the threat to human health posed by overdiagnosis and the waste of resources on unnecessary care.”