Australian researchers have a proposed method of evaluation to help identify a potentially problematic test
As exciting as new technology is, the introduction of more sensitive tests has been a major driver of overdiagnosis and potential harm.
But now Australian researchers have a proposed method of evaluation to help identify a potentially problematic test.
Professor Alexandra Barratt, epidemiologist and lead investigator of the Australian overdiagnosis research group Wiser Healthcare, helped to develop this framework after recognising the potential long-term and irreversible damage that can be caused by unnecessary tests. Thyroid cancer is a classic example where advances in technology have led to the detection of hundreds of thousands of previously hidden “cancers” across the population, but where later analyses has revealed the vast majority of these cancers, if they had been left untreated, would not have advanced to have caused any significant morbidity or mortality.
“Overdiagnosis relies on the existence of a population reservoir of detectable disease and the availability of tests capable of ‘unearthing’ cases from that reservoir,” Professor Barratt and her team explained.
“We’re used to thinking of cancers as a uniformly fatal, progressive disease, but what we’re finding is that one way to think about it is that it is actually a new form of cancer and maybe it does not actually warrant that same word,” the professor of public health at University of Sydney said.
“In a way what we’re doing is creating new diseases but we’re using old labels for them,” she said.
To determine whether it was possible to evaluate the risks of potential overdiagnosis and overtreatment versus benefit, the researchers looked at a new blood test for acute coronary syndrome – highly sensitive cardiac troponin (HS-cTn) and asked these five questions of it:
1. Could this test diagnose more people?
In a large Scottish trial, the introduction of HS-cTn led to more people being told they had myocardial injury or infarction than with the previous assay.
2. Does clinical practice change with the test?
In the case of this assay, more patients were given additional tests and medication as a result.
3. Are the new patients asymptomatic or at low risk?
The key here is to look at the ratio of incidence to deaths, and if it gets lower (that is, the mortality remains the same while the number of people with the diagnosis increases) without an obvious improvement in treatment, overdiagnosis is likely to be the case. Despite more people being treated, the rates of heart attack deaths remained the same over the following year.
4. Are more people being treated?
Being labelled with a disease or condition carries both a psychosocial burden and also commonly commits people to undergoing potentially harmful tests and treatments. Additional coronary angiograms and anti-platelet therapy can certainly cause harm.
5. Do the harms outweigh the benefits?
The lack of data around new tests, compared to new medications, is one of the key reasons Professor Barratt and her team are calling for the introduction of this framework.
While it wasn’t possible to say whether the introduction of HS-cTn was causing overdiagnosis, the team said there were sufficient red flags to warrant further investigation.
Rather than simply assuming diagnostic technology would be a net positive, the key to preventing harms would be to assess the risk-benefit ratio before introducing it into the healthcare system, or introducing it on a provisional or a short-term basis, Professor Barratt said.
Because modern medicine has such obvious benefits, it was easy to overlook harms, and so a clear framework to evaluate tests would help be more agile in curtailing harms of new tests as they appeared, she said.
Ann Intern Med 2019; online 5 February
