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Alt-One-More t1_ixn4qzn wrote

What you're looking for is in the article linked:

"Approximately 1.6% of individuals in the United States will develop pancreatic cancer during their lifetime.1 With this relatively low prevalence, even an ideal screening test with 99% sensitivity and 99% specificity would yield 1000 false-positive results if applied to 100 000 patients. These false-positive results would require subsequent diagnostic evaluation and accrue additional complications, costs, and patient distress that would cause the risks of screening to outweigh any potential benefit."

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_Oman t1_ixn6ufq wrote

Replying to Alt-One-More (#653,725)

The simple version: If the screening were perfect, it would help immensely. When screening isn't perfect and the occurrence rate is is low, screenings can create worse overall outcomes for the general population.

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Prince_LunaShy t1_ixng67c wrote

If screening was 100% accurate with no false negatives or positives, it'd be fine. In reality, if you test 100,000 people, maybe 1000 of those tests are probably wrong, one way or the other (depending on the test ofc). You also have no way to tell which ones are likely to be accurate because it's a random screening and not someone with an identified issue. Especially with diseases/conditions that are rare, this makes screening both innefective and overly expensive, as the false negatives and positives will require further involvement to correct.

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PolarSquirrelBear t1_ixnh2ty wrote

Replying to _Oman (#653,903)

It’s why they won’t test for herpes unless you’re symptomatic. There are so many false-positives you would completely change your life around it, with a possibility that you don’t actually have it.

But with the prevalence of it, you can pretty much just assume you have it anyways.

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NikeDanny t1_ixnyqvd wrote

As others have said, its about the false negatives, causing harm.

Additionally, screening Methods themselves arent harmless, sometimes. I dunno the specifics of pancreatic cancer screening, but, eg., the colonoscopy checkup every 10 years is invasive in itself. While you provide a (proven) benefit to every 6 of 1(00?).000 patients, you also cause severe complications (bleeding, death) to 3 of 1(00).000. While in this case, you have a net sum of 3 people being helped (prolly being more since you could manage some complications, I think), it may not be the case for rarer cancers.

If for fishing out 1 out of 100k [obscure cancer] you have to hurt 2-3 out of 100k, its just not worth it. Not to mention since screenings usually are not gold proofs, you need to do actual diagnostics, which can be hurtful in terms of (minimally-)invasive procedures, high radiation exposure and hospitalization stays.

We have to wait until we get something that allows us to diagnose a patient with 100% accuracy while having no drawback for those rarer cancers, sadly.

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No_Management9536 t1_ixov9ni wrote

Replying to [deleted] (#657,244)

It is not a question of the test being or not Good enough, it depends on the population. Even 99% S/S tests when applied to a population with very low risk of being sick will result in false conclusions. That’s why we must consider the “pre-test probability”, which is basically the presumed prevalence. If you take a pregnancy test and use it in young females sexually active with their periods delayed, and then use the same test in nuns with regular periods, the accuracy will be very different.

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