Controversy continues to swirl over chest CT scans to screen for lung cancer.
MedPage Today reports on a recent study that continues to suggest that it isn’t ready for general use yet. Not surprisingly, CT scans had more false positives than traditional chest x-rays when used to look for pulmonary masses.
The probability of a false positive was 21 percent after one scan, and 33 percent after two. This is a huge number, and can lead to unnecessary patient anxiety, and worse, invasive testing such as lung biopsies for conditions that eventually turn out to be benign. These follow-up tests have real risks, such as bleeding, pneumothoraces, and infection.
This not only corroborates the lack of current evidence suggesting any mortality benefit to the early detection of lung cancer, but shows that indeed, “there is a small, but real potential for harm from screening.”
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{ 4 comments }
CT scan generates more data than a Chest Xray. Whenever there is more data, there are bound to be more false positives. But I agree, screening using CT scan is probably not wise.
From someone who is used to having a lot of tests performed, I’d rather be given a tentative diagnosis that is later reversed than allow a potential problem to develop, even if that likelihood is as low as 10%. For all of the anxiety that the tests may erroneously cause, how many lives saved or improved does it take to justify? One, a hundred? The only way I will agree with you is if you can say that CT’s do not improve actual cancer detection at all. How self-centered do you have to be to say CT’s are worthless only because you were one of the ones who were tested false-positive? There is some flawed logic here.
Lets not forget about the human costs of false positives (from complications associated with diagnostic testing), but false positives also serve to inflate health care costs. More testing means more spending. And more spending means insurers (or governments) takes on more financial risk when providing health coverage.
The more costly a population is to insure, the higher premiums (or, in the case of single-payer, taxes) will be, and de facto rationing (when premiums become unaffordable for some) or actual rationing (as in the NICE of the UK) inevitably occur. If inflated health care costs are preventing other members of society from accessing care, is a false positive rate of more than 30% still justifiable?
Christi,
It’s not just anxiety even if anxiety may not be so good for your blood pressure or heart.
It’s also real physical complications of invasive tests that are triggered by these false positives. 21% risk or 1/5 chance of false positive that leads to a test that may have 1/1000 risk of serious complication. Multiply these two numbers and you’ll get 1/5000 chance of a complication from the test. Would you take 1/5000 risk of a complication that may be even fatal vs one in a thosand chance of early detection which may or may not help? Which may even result in overdiagnosis i.e. find something that looks like cancer under a microscope but would’ve never grown in your life time?
Now this is from a single test. But if you do these tests regularly, than a chance of having at least one false positive during these 10 years will be almost a guarantee. After only 3 years, it’ll already be around 50%; after 5 years – around 80%.
Also your estimate of 1/100 chance of benefiting from a test is widely unrealistic. Even for tests that are shown to save lives e.g. mammograms it’s often 1/500 after 10 years of screening and that is a very optimistic and often disputed number. For lung cancer screening there isn’t even a single study that showed that it reduces mortality from cancer at all.
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