Earlier quoted context omitted.
A big part of this is the fact that learning information (about a disease or condition) early is often NOT the same thing as learning information that will change a patient’s clinical outcome.
I never understood this. I mean I totally get the concept, but I don't get how it came to influence policy. Put it like this: how many people are you willing to kill to make sure people don't find out they're sick? Because that's what it boils down to. And it sounds... sociopathic.
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.