3 TIMES'S THE CHARM?

[GLORIAmunchkin72]

How many times do they have to shove something up your nose in order to know if you have it or not (COVID19)? I'm refering to the people who test positive one day and negative the next.

[GrumpyRN, NP]

22 minutes ago, GLORIAmunchkin72 said:

I'm refering to the people who test positive one day and negative the next.

If you test positive one day what possible reason would you have to re-test the next day?

The test has something like a 30% false negative rate so if you're positive you're positive, it doesn't just magically disappear.

[GLORIAmunchkin72]

The same reason people take lie detectors more than one time. One test would say you lied and the next test would say you didn't and maybe a 3rd test would prove inconclusive. Sorry. Couldn't think of a better analogy.

[GrumpyRN, NP]

3 minutes ago, GLORIAmunchkin72 said:

The same reason people take lie detectors more than one time. One test would say you lied and the next test would say you didn't and maybe a 3rd test would prove inconclusive. Sorry. Couldn't think of a better analogy.

But if you're positive for a virus you are positive for a virus.

A lie detector test is pretty much a subjective thing but an actual "we have found evidence of infection" is pretty objective and not subject to change.

I will grant you you may (and it is a very big may...) get a faulty test or testing machine but my point still stands, if you have tested positive why are you re-testing?

[GLORIAmunchkin72]

I never have (but some people do).

[JKL33]

1 hour ago, GrumpyRN said:

But if you're positive for a virus you are positive for a virus.

No...?. This all has to do with the sensitivity, positive predictive value, etc. of the molecular tests. 4 basic possible results of a test (generally-speaking here): 1) Person with condition (correctly) tests positive 2) Person w/ condition (incorrectly) tests negative 3) Person without condition (incorrectly) tests positive 4) Person without condition (correctly) tests negative.

In areas of low suspicion or with mass testing (I.e. testing people without sx or who have very low known exposure etc.) then the positive predictive value of the test is not as high as it would be in areas of higher prevalence.

Here is an article that discusses this in simple terms https://theconversation.com/the-positives-and-negatives-of-mass-testing-for-coronavirus-137792

[GrumpyRN, NP]

2 hours ago, JKL33 said:

No...?. This all has to do with the sensitivity, positive predictive value, etc. of the molecular tests. 4 basic possible results of a test (generally-speaking here): 1) Person with condition (correctly) tests positive 2) Person w/ condition (incorrectly) tests negative 3) Person without condition (incorrectly) tests positive 4) Person without condition (correctly) tests negative.

In areas of low suspicion or with mass testing (I.e. testing people without sx or who have very low known exposure etc.) then the positive predictive value of the test is not as high as it would be in areas of higher prevalence.

Here is an article that discusses this in simple terms https://theconversation.com/the-positives-and-negatives-of-mass-testing-for-coronavirus-137792

Again I am going to repeat; If you test positive for the virus why would you re-test???

You behave as if you are positive, you get on and isolate and be thankful you have/had a symptom free/mild episode. You may find out later with an antibody test that you had a false positive but so what?

I would also like to take this opportunity to thank you for giving me "an article that discusses this in simple terms." After all, as I am just an Emergency Nurse Practitioner, been a nurse for 35+ years and have a degree from one of the better UK universities it would appear you seem to think my understanding is poor and I know nothing about false positives, viral load, infection control or infection vectors etc.

[JKL33]

17 minutes ago, GrumpyRN said:

Again I am going to repeat; If you test positive for the virus why would you re-test???

I suppose one scenario could be if you were completely asymptomatic but participated in mass screening/testing in an area of low prevalence, then you might have an interest in getting a better idea of the (possibly minor, possibly more substantial) inconveniences/hardships that would result from a true positive.

Moreover, it's in the interest of science to know this information, if/when it is possible to obtain it. It is relevant to several other topics, such as all the talk about asymptomatic vs. presymptomatic spread, as well as basic understanding of the virus (e.g. How many people have the virus and truly have no symptoms?--Well how would we ever figure that out if we can't accurately determine that they actually had the virus?)

30 minutes ago, GrumpyRN said:

I would also like to take this opportunity to thank you for giving me "an article that discusses this in simple terms." 

I'm sorry. It was not intended to be hurtful in any way; I've read a lot of more scientific things while all this has been going on and frankly I prefer not to get as bogged down in every single discussion. I posted it for my own benefit as well as anyone else who doesn't have time or inclination to do what epidemiologists do for a living. I tried to broadcast my tone by using a smiley right up front, but obviously that failed.

However, seeing your reaction, I will point out that despite your experience you posted blatantly incorrect information:

4 hours ago, GrumpyRN said:

But if you're positive for a virus you are positive for a virus.

And if you actually have that virus/illness then the test was correct. If you actually don't, then it wasn't.

4 hours ago, GrumpyRN said:

The test has something like a 30% false negative rate so if you're positive you're positive,

Can you explain? I don't understand the relevance/connection.

Thank you.

[GrumpyRN, NP]

5 minutes ago, JKL33 said:

However, seeing your reaction, I will point out that despite your experience you posted blatantly incorrect information:

No, if you test positive for the virus then as far as you and the world are concerned you have the virus whether it is false or not. You do not need to re-test.

6 minutes ago, JKL33 said:

Can you explain? I don't understand the relevance/connection.

I have worded it badly. If ~30% are false negative that means all negatives and 30% of positives will be treated as negative therefore having a positive result means you are much more likely to actually have the virus than not, see my comment above. Having a negative test is not absolute confirmation that you are virus free. Therefore practically, ignore the term false positive and treat every positive as true.

I'm not sure what is happening in your part of the world but here the virus is ageist, sexist and racist. Effects older people, males more than female and ethnic minorities more than white. So younger people can be symptom free and infected - one of the arguments against re-opening schools.

[JKL33]

31 minutes ago, GrumpyRN said:

No, if you test positive for the virus then as far as you and the world are concerned you have the virus whether it is false or not. You do not need to re-test.

Yes. As a practical matter I agree. But perhaps that generally works best when the person tested has a significant reason they want to be tested, such as having very mild atypical sx but living with a very high risk individual. Then, sure, if they're going to be tested then they might as well come at it with the idea that they will take a positive as being a true positive unless the testers or medical providers have a reason to question their particular result.

A few people, though, (and I admit/understand that false negatives are generally more common than false positives), could really face hardship from a false positive when the pretest probability is very low (prevalence is low), such as a case where a random employer mandates testing as part of a cooperative community effort or a person individually agrees to be tested in response to a community campaign for epidemiological purposes or whatever. Then you may end up with a few here and there who unexpectedly test positive and want to know more about their situation due to the downstream effects of a positive result, such as being told they can't come to work or feeling as if they shouldn't be providing care to an at-risk loved one, etc.

31 minutes ago, GrumpyRN said:

So younger people can be symptom free and infected - one of the arguments against re-opening schools.

Yes, definitely. And I think it's important that we understand more about these people and especially the extent to which they spread the virus. But...I still do think that we have to be aware of the small potential for false positives as well as the more common false negatives. Honestly, for better understanding of the virus, people who are completely asymptomatic and test positive do kind of warrant confirmatory testing -- and even further follow-up if possible. That (?) seems like it would go a long way to helping with the question of how much spread happens via asymptomatic individuals as well as how many will remain asymptomatic vs. actually in retrospect were presymptomatic when they tested positive.

I don't know...interesting and overwhelming.

Thanks for your answer.

[GrumpyRN, NP]

15 hours ago, JKL33 said:

A few people, though.... could really face hardship from a false positive

This is unfortunately a difference in our two countries, in UK they would be eligible for sick pay (in NHS eligible for 6 months full pay then 6 months half pay when off sick) so people are less resistant to being off work even when they are not actually sick. In US there are real hardships.

As you say, interesting and overwhelming.

Remember the old Chinese curse - "May you live in interesting times." These are very definitely, by any measurement used, "interesting times."

Stay safe.