If you gave a mammogram to every 20 year old woman, you would end up doing a large number of unnecessary biopsies and you’d find almost no real cancer. In the end, you’d lose more people than you would save.
Or that’s the idea. I’m no expert in this but it makes sense to me conceptually.
If you gave a mammogram to every 20-year old, you wouldn't do a biopsy when you got a positive. You'd increase monitoring and maybe suggest lifestyle changes. The same way we don't immediately catherize everyone who comes back with high cholesterol.
The problem is that it compounds quickly.
Consider:
* For a rare condition you need a lot of tests to find them. Let's say you look for something that 1 in a million can be expected to have.
* When you find those 1 in a million, the testing needs to save them, which means a proportion of them need to otherwise be significantly affected. Let's say 1 in 10 of them die.
* When you find those 1 in 10 million that has the condition that would have died without intervention, early intervention needs to actually make a difference. Let's say 1 in 10 of those actually survive because of early detection.
Now you have to do ~100 million tests to save one life.
Suddenly 100 million:1 odds of dying as a result of a visit to do a blood test are enough to neutralise the benefit, be it infections or accidents etc.. And that includes secondary effects such as delayed diagnosis because a false negative leads a patient to delay seeking a second opinion once symptoms present.
Additionally there's the opportunity costs in terms of saving lives by spending the money elsewhere, such as e.g. awareness of symptoms and the like, or addressing entirely different issues.
Of course, if you have a more common condition, and/or a condition that is much more lethal, and/or a condition where early intervention makes a difference, this all changes.
But it's worth noting how little mass screening we do - as it turns out, it's hard to find conditions where the benefits are substantial enough to be worthwhile. In some cases, such as the use of mass screening for breast cancer, there has been calls to scale it back some places because it was unclear whether there was a net benefit.
Testing doesn't kills by itself, not in numbers worth mentioning. Treatments - sure, a whole different ball game, they're positively dangerous. But between testing and treatments there should be a specialist that crunches the numbers and comes to a decision. Which, like in the mammogram example above, is not always going to be more aggressive testing.
What testing does is give you more information, which in a remotely sane system should lead to better decision making. Of course, I can imagine insane systems where, for example, the patient decides, the insurance pays and the doctor can be sued for discouraging treatments. In this particular combo you probably want to avoid doing mammograms to 20 yo, because the chance of a false positive is 1%, the chance of a true positive is 0.01%, and you end up with perverse chains leading to healthy people doing chemo. Like I said in the original comment, I GET the phenomenon. What I don't get however is how it can get even close to conventional wisdom that you want to avoid testing, as a rule. That's a particular fix to a particularly insane incentive combo, and common sense should make everybody rail against the insane incentive combo, and not act like the niche fix is actually a goal.
I can't really explain how this came to be. Maybe people stumbled on an explanation of how extra testing _may_ be harmful, and the idea was so cool that it got stripped of context and became a meme in itself.
Mammography involves radiation and pressure. The radiation alone is a significant risk [1], and kills by causing cancer. It can also cause tumors to rupture and spread malignant cells. It's significant enough to significantly increase the hurdle where mammography is justified. It does not mean it never is - absolutely not. But it means screening programs need to be targeted.
> What I don't get however is how it can get even close to conventional wisdom that you want to avoid testing, as a rule.
It's not conventional wisdom that you want to avoid testing. That is for example what led to a lot of really aggressive campaigns for extensive breast cancer screening.
What we saw was a small improvement in outcomes on a small number of positive test results, for a level of testing that suggested it was necessary to take into account other factors.
Breast cancer screening was rolled back many places, or widening of the age bracket was halted as a result of looking at outcomes and realising that "conventional wisdom", which used to be that more testing was inherently good was flawed.
There are clear, quantifiable harms from it, ranging from actual risks of causing cancer or causing spread of cancer with mammography. These risks are low enough to be worth it for certain patient groups, but high enough to add up to problems if screening is too widespread.
People didn't start worrying about this because it was "conventional wisdom", but because the data shows people actually dying.
What I'm advocating for btw, just to make clear, is regularly showing up to a doctor who will recommend all the cost effective non-intrusive tests (like blood work) plus the intrusive testing depending in your particular risk profile. This doesn't seem like a controversial opinion to me - more like a common sense default.
As for conventional wisdom, look at this thread. Count the pro/contra comments if you want. Other then a tautological "some medical procedures can be dangeours if misused/overused", I still don't get how people can be against testing, in general.
It points out exactly why broad, indiscriminate screening can not be assumed to be safe, and that "optimizing the process" means moving away from thinking that more screening is automatically better, and towards identifying which groups where the benefits outweigh the dangers.
But the main reason for posting that link was to point out that the idea that testing does not kill is false for some types of testing, and as such you need to understand the risk vs. reward, or you may end up doing harm.
> What I'm advocating for btw, just to make clear, is regularly showing up to a doctor who will recommend all the cost effective non-intrusive tests (like blood work) plus the intrusive testing depending in your particular risk profile. This doesn't seem like a controversial opinion to me - more like a common sense default.
I haven't seen anyone here arguing against that. That's not what's been discussed by those of us here pointing out the dangers of mass-screening.
A great example is prostate cancer. It often gets detected now, people are informed they have cancer, but most often the correct answer is "watchful waiting", i.e. no treatment, probably forever. But people now know they have cancer, and are frightened, because cancer, and thus press for treatment. But this comes with a 10-90%(!) chance of incontinence and 50-90% chance of erectile dysfunction - for a cancer that most probably wouldn't have caused them bigger problems for their whole life.