Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

When they warn of rare disorders, these prenatal tests are usually wrong

nytimes.com

Post reply on HN
Print view View original

11–20 of 176 posts

Re: When they warn of rare disorders, these prenatal tests are usually wrong

#11

Post by bdzr »

sklargh wrote: post #3

I recall a period in the early 2000s when unindicated whole-body CAT-scans were being advertised on television. That got knocked down pretty quickly but wow a lot of folks picked up a big chunk of their lifetime radiation allowance because of that. These tests seem to operate under a similar model, disregard the risks of unnecessary testing in return for information of limited utility that may cause material harm.

I think you're conflating "these tests cause harm" e.g. radiation and "the information gleaned from these tests could cause the patient to make poor decisions". Having a regulatory body make this value judgement for people has quite a bit of disadvantages. See "DON’T TRY THIS AT HOME: THE FDA’S RESTRICTIVE REGULATION OF HOME-TESTING DEVICES" https://scholarship.law.duke.edu/cgi/viewcontent.cgi?article....

Re: When they warn of rare disorders, these prenatal tests are usually wrong

#12

Post by sjckciodjcr »

This article seems a bit deceptive. We are going through NIPT soon and our doctor went over false positive and false negative rates for the common screens. Our doctor has pointed out some of the screens (esp for rare conditions) are not that accurate. The only procedure with high accuracy, amniocentesis, has a slight risk of miscarriage (our provider quoted 0.3% ) so its still statistically better to take NIPT and then only consider amniocentesis with a positive result since there is no risk from NIPT.

You are supposed to treat a positive on NIPT as “there’s a chance your baby has this, need a more accurate procedure to confirm”.

It sounds like their ob gyn wasn’t able to explain results to them or they didn’t understand the probabilities. To be fair our provider didn’t even suggest tests for the disorders in the article, probably because of the false positive rates and rarity. Sounds like these extra screens shouldn’t be offered.

Re: When they warn of rare disorders, these prenatal tests are usually wrong

#13

Post by treis »

inglor_cz wrote: post #8
treis wrote: post #4

This seems to miss the point entirely. Even for their worst example the odds of the fetus having it go from 0.005% to 7%. That's valuable information even if it's not perfect or somewhat hard to understand.

This would be valuable for running some extra tests (possibly more expensive, but more accurate), but not for, say, decision to abort the kid, which is what usually "hangs in the air" after such a test result.

That depends on the person though doesn't it? I'm not sure what I'd do in that situation. But 7% seems awfully bad odds for painful and debilitating life.

Re: When they warn of rare disorders, these prenatal tests are usually wrong

#14

Post by Enginerrrd »

bdzr wrote: post #11
sklargh wrote: post #3

I recall a period in the early 2000s when unindicated whole-body CAT-scans were being advertised on television. That got knocked down pretty quickly but wow a lot of folks picked up a big chunk of their lifetime radiation allowance because of that. These tests seem to operate under a similar model, disregard the risks of unnecessary testing in return for information of limited utility that may cause material harm.

I think you're conflating "these tests cause harm" e.g. radiation and "the information gleaned from these tests could cause the patient to make poor decisions". Having a regulatory body make this value judgement for people has quite a bit of disadvantages. See "DON’T TRY THIS AT HOME: THE FDA’S RESTRICTIVE REGULATION OF HOME-TESTING DEVICES" https://scholarship.law.duke.edu/cgi/viewcontent.cgi?article... .

This isn't really a fair criticism. I could be wrong, but I believe your comment reflects a bit of naivete about the current state of evidence-based medicine.

To evaluate the value of performing a diagnostic test as an intervention, you DO have to look at final actual patient outcomes at an appropriate end target which includes sending people unnecessarily down different treatment paths, including additional testing with additional risks. And most importantly is that, in fact, mere knowledge of diagnostic results has been PROVEN to cause harm in many scenarios.

Now... if a patient WANTS that test, I think it should be available. But whether or not it should be performed routinely without prompting is an appropriate question for regulatory bodies.

Re: When they warn of rare disorders, these prenatal tests are usually wrong

#15

Post by bscphil »

gwern wrote: post #9

This article is a confused mess. It's something of a Gish gallop in conflating all the different issues they could come up with, while leaving out all the necessary vocabulary (C-f "Bayes" "posterior" "decision theory" [Phrase not found]) making it almost impossible to consider each issue in adequate detail. It mixes up poor communication (reporting false-positive/negative rates as if posterior probabilities, & exagg…

They even missed "base rate", which is the way I usually see this explained to ordinary people without stats backgrounds. Really disappointing.

Re: When they warn of rare disorders, these prenatal tests are usually wrong

#16

Post by hn_throwaway_99 »

gwern wrote: post #9

This article is a confused mess. It's something of a Gish gallop in conflating all the different issues they could come up with, while leaving out all the necessary vocabulary (C-f "Bayes" "posterior" "decision theory" [Phrase not found]) making it almost impossible to consider each issue in adequate detail. It mixes up poor communication (reporting false-positive/negative rates as if posterior probabilities, & exagg…

> implicit calls for the FDA to Do Something and ban the tests (not an iota of cost-benefit considered nor any self-reflection about whether we want the FDA involved in anything at all these days)...

This is true in so many areas of journalism but lately seems especially egregious in the NYT. And I don't really blame them, as the incentives for any individual reporter are just too great - having the government make a major policy change based on your article is basically the brass ring for an investigative reporter.

I basically can only use these types of articles as a jumping off point for my own research, as I usually find the moralizing conclusion the article comes to as unsupported.

Re: When they warn of rare disorders, these prenatal tests are usually wrong

#17

Post by sjckciodjcr »

inglor_cz wrote: post #8
treis wrote: post #4

This seems to miss the point entirely. Even for their worst example the odds of the fetus having it go from 0.005% to 7%. That's valuable information even if it's not perfect or somewhat hard to understand.

This would be valuable for running some extra tests (possibly more expensive, but more accurate), but not for, say, decision to abort the kid, which is what usually "hangs in the air" after such a test result.

NIPT is not supposed to be used for termination decisions. A positive is meant to be “your baby might have this, test further with amniocentesis”.

Re: When they warn of rare disorders, these prenatal tests are usually wrong

#18

Post by lostlogin »

Neil44 wrote: post #6

Before my daughter was born I sometimes felt like it was the doctors job to scare us with every worse case scenario possible. It was quite stressful and upsetting.

I'm not certain that perk of parenthood ends at birth.

Re: When they warn of rare disorders, these prenatal tests are usually wrong

#19

Post by SpicyLemonZest »

sjckciodjcr wrote: post #12

This article seems a bit deceptive. We are going through NIPT soon and our doctor went over false positive and false negative rates for the common screens. Our doctor has pointed out some of the screens (esp for rare conditions) are not that accurate. The only procedure with high accuracy, amniocentesis, has a slight risk of miscarriage (our provider quoted 0.3% ) so its still statistically better to take NIPT and th…

"These extra screens shouldn't be offered" seems like exactly the point the article is trying to make.

Re: When they warn of rare disorders, these prenatal tests are usually wrong

#20

Post by halpert »

How did this article, written by someone who clearly lacks an understanding of basic statistics, make it into the Upshot? They try to make it seem like the test is wrong 85% of the time, but that's not necessarily the case. All we know from the article is that 85 / 100 positive results are false positives, which means the test could actually be quite accurate. If the test correctly identifies 100% of real cases, then that sounds like an excellent test. Just as an example, if 1/4000 people have the disease, and the test identifies 100% of these cases, then around 0.14% of test takers will get a false positive.
Post reply on HN