alt Hacker News> as much as my health anxiety would love another set of CT scans to feel relieved about, even if they do find something potentially interesting it may be worse to act on it than to do nothing
I personally have a preference for having the maximum amount of information available to make a decision.
“Don’t get that “unnecessary” test, it might give you a result that might lead to treatment you don’t need” — hearing this blows my mind every time.
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Worth keeping in mind that no medical test has a false positive rate of zero, so whether a test is worth doing becomes a statistical question - and the accuracy of some of those tests is different depending on whether a doctor first screened you to be likely to have a certain condition.
If you were to do something like run every cancer test possible then _eventually_ you'll find one that says you have cancer, but it's not a valuable result because statistically one of them was eventually going to say that. I don't think most doctors are doing significant statistical analysis to determine what tests to give you, but the general concept that you don't simply run every test you can for fun is very sound, screening beforehand can rule out a significant amount of false positives while hopefully not significantly increasing the chance that something is missed.
As somewhat more real example, rapid strep throat tests overall rarely give an inaccurate positive result, meaning that if the test shows a positive result you can be pretty confident you have strep throat and need antibiotics. However the false positive rate of rapid strep throat tests is extremely dependent on the patient first being screened for symptoms of strep throat - there are lots of asymptomatic strep throat carriers who have no symptoms but do have the bacteria, they don't need treatment but do give a positive result on the test. Thus if you were to give a rapid strep throat test to an entire school to try and eliminate all cases of strep throat then you'd find that ~10% to ~20% of the school gets a positive result. In that situation at least the tests are cheap and you could potentially resolve the situation over a number of weeks, but not every test is so simple.
Having the maximum amount of information assumes you know which information is useful and relevant. That isn’t always clear in medicine.
Treatments you don’t need can be worse than no treatment.
Assuming you're not a specialized doctor, you're in no position to interpret that information. The person doing the interpreting usually has incentives that are perfectly misaligned with yours. And even assuming no malice, medical professionals tend to overestimate the benefit and underestimate the risk of the procedures they specialize in. One would hope that doctors would be required to be great statisticians, but alas..
The treatment you don't need might be zero risk, but it might also have quite a bit of it. And some tests carry risks too: See how different countries have very different protocols. The US system, which is colonoscopy first, and where polypectomies will be done at the same time, can end up with bowel perforations when the polyp was not even cancer. So the diferente treatment protocol is not just about costs, but about balancing different risks.
The unnecessary test, leading to an unnecessary intervention, which gets you unnecessary long term issues is a real risk in many cases. It's not just a matter of doing a bonus blood test here or there.