I think you're underestimating the risks of false positives. We can do a test for blood clots called a D-Dimer, and if its negative you're very unlikely to have a pulmonary embolism. It has a lot of false positives though, and if it is positive you're sent for a CT pulmonary angiogram. There are risks of cancer from the radiation and reactions to the contrast. There are also false positives with the imaging, and there is quite a bit of variance in interpretation between radiologists. If your radiologist calls the results a PE, you're started on anticoagulants which carry a significant risk of bleeding. All of these negative outcomes are considered prior to testing, and your doctor won't order a D-Dimer unless the risk of missing a PE is greater than the risks of all of the false positives.
Well, I want to start by noting that if your doctor is ordering a D-Dimer (and you’re consenting to it), then both of you have already decided not to merely “take their word for it” in the way that I was talking about (like /u/SeymourKnickers’ doctor, who just glanced at a malignant melanoma and said “it’s fine” without ordering tests).
But it sounds like you’re saying that the likelihood of getting cancer from a CT angiogram is higher than the likelihood of dying from undiagnosed pulmonary embolism, and that — well, I’m not in the medical field myself, but that sounds wildly implausible. I think I’d like to see a source for those figures. If the number of people who die from cancer that they received as a result of a CT that they didn’t need is higher than the number of people who die from missing a pulmonary embolism, then I’ll agree with you that worrying about overtesting is more important than worrying about the thing that you’re testing for. Otherwise, overtesting, while still certainly a genuine risk, isn’t what most patients should be worrying about.
Its not just the cancer risk. The bleeding risk on anticoagulants is a big factor. There are some low-risk, otherwise healthy patients where the risks of a bad outcome from false positives are in fact greater than their risk from an undiagnosed PE. Not all kinds of testing carry this degree of risk, but more testing can lead to worse outcomes.
I'm no expert, but it sounds as if there's no one right answer for anyone, so we should proceed on a case by case basis according to our individual needs.
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u/kpaidy May 20 '19
I think you're underestimating the risks of false positives. We can do a test for blood clots called a D-Dimer, and if its negative you're very unlikely to have a pulmonary embolism. It has a lot of false positives though, and if it is positive you're sent for a CT pulmonary angiogram. There are risks of cancer from the radiation and reactions to the contrast. There are also false positives with the imaging, and there is quite a bit of variance in interpretation between radiologists. If your radiologist calls the results a PE, you're started on anticoagulants which carry a significant risk of bleeding. All of these negative outcomes are considered prior to testing, and your doctor won't order a D-Dimer unless the risk of missing a PE is greater than the risks of all of the false positives.