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Antibody tests

This topic has been archived, and won't accept reply postings.
 Eric9Points 20 May 2020

I hear Superdrug are selling them.

Even if they are not that accurate if I took three tests over three days and got the same result each time I'd have an accurate test, yes?

2
 Luke90 20 May 2020
In reply to Eric9Points:

> Even if they are not that accurate if I took three tests over three days and got the same result each time I'd have an accurate test, yes?

Not necessarily, no.

 Eric9Points 21 May 2020
In reply to Luke90:

Well even if the test just gave random results the chances of getting three in a row is 8/1.

If it's 80% accurate it's <1% chance of being wrong.

20% of 20% of 20% of being wrong?

7
 Blunderbuss 21 May 2020
In reply to Eric9Points:

They are given as 97.5% accurate...sold out though. 

 jimtitt 21 May 2020
In reply to Eric9Points:

You do understand the test shows whether you had the virus 2 or 3 weeks before, not whether you've "got it"?

1
 elsewhere 21 May 2020
In reply to Eric9Points:

> Well even if the test just gave random results the chances of getting three in a row is 8/1.

> If it's 80% accurate it's <1% chance of being wrong.

> 20% of 20% of 20% of being wrong?

Only if the three tests are independent, but the three tests are not independent so they are more likely to share a common mode of failure.

They are being done on one person who might by some quirk of immune response tests falsely negative. Or the person repeats  the same mistake three times and doesn't do the test very well. Or some other single fault that is common to all three tests.

PS since you mention random, try my free test  that is BETTER than 80% accurate.

Roll a dice. If not 6 you are virus free. 

At any one time few people infected (less than 100,000 in 66,000,000 in UK?) so my free dice test gives the right negative for virus result 83% of the time.

Post edited at 06:41
 marsbar 21 May 2020
In reply to Eric9Points:

It's not a random 20% of tests that are broken, it's more like tests can't measure it in 20% of people.  You may get a different result if you did 3 tests 2 weeks apart. 

Given that we don't actually know if the antibodies give immunity I don't think there is much point in individual testing. 

 MargieB 21 May 2020
In reply to marsbar:

If you have had Covid 19 intensely , get over it, are later exposed and have minor symptoms, is that the body building long term immunity? I presume one is still infectious with minor symptoms and should isolate, but over time, with  perhaps further exposure, enough immunity is built in the body? I'm not a doctor but is someone medically minded on this one?

Post edited at 07:52
 Arms Cliff 21 May 2020
In reply to marsbar:

> Given that we don't actually know if the antibodies give immunity I don't think there is much point in individual testing. 

This is the key thing, as per this article https://www.theguardian.com/world/2020/may/20/healthcare-staff-to-get-coronavirus-antibody-tests-from-next-week

 “But we must be clear that huge uncertainties remain while we do not know the level and length of any immunity which antibodies will offer.”

In reply to Eric9Points:

> I hear Superdrug are selling them.

> Even if they are not that accurate if I took three tests over three days and got the same result each time I'd have an accurate test, yes? <

I'm no expert, but it might be more likely to be accurate if the three tests were positive than if they were all negative, Only a matter of degree though. But then presumably you may well be hoping for reassurance that you are possibly immune/resistant yourself and also less likely to infect others.

1
 Eric9Points 21 May 2020
In reply to jimtitt:

> You do understand the test shows whether you had the virus 2 or 3 weeks before, not whether you've "got it"?

Yes.

 Eric9Points 21 May 2020
In reply to marsbar:

> Given that we don't actually know if the antibodies give immunity I don't think there is much point in individual testing. 

The evidence we do have, as I understand it, suggests that it does at least for some time.

 marsbar 21 May 2020
In reply to MargieB:

I have no idea beyond what I saw on this weeks Horizon (it's on iplayer).  The scary possibility was that it may be that people could be immune enough to be symptom free but still infected enough to infect everyone around.    

Interesting question.  

 marsbar 21 May 2020
In reply to Eric9Points:

> The evidence we do have, as I understand it, suggests that it does at least for some time.

I hope so.  Do you happen to remember where you saw that? 

 Eric9Points 21 May 2020
In reply to elsewhere:

> Only if the three tests are independent, but the three tests are not independent so they are more likely to share a common mode of failure.

> They are being done on one person who might by some quirk of immune response tests falsely negative. Or the person repeats  the same mistake three times and doesn't do the test very well. Or some other single fault that is common to all three tests.

Ok, then it's necessary to understand how the test works and evaluate the mights and maybes.

 neilh 21 May 2020
In reply to Eric9Points:

What a waste of money using them.

What exactly is the point? Great you have had it. Are you immune....err based on the science there is no proof you are immune.

What are you going to do with the results???

Please emlighten me what is the benefit to you of getting the test done.

 Eric9Points 21 May 2020
In reply to marsbar:

Somewhere on Twitter.

The point is that people don't get C19 twice.

There were reports that people did but these seem to have been put down to errors in testing as far as I remember.

1
 kipper12 21 May 2020
In reply to Eric9Points:

Do you know what the performance characteristics are?

 WaterMonkey 21 May 2020
In reply to Eric9Points:

No but you'd be £207 lighter

 ianstevens 21 May 2020
In reply to Eric9Points:

> I hear Superdrug are selling them.

> Even if they are not that accurate if I took three tests over three days and got the same result each time I'd have an accurate test, yes?

Repeatability is not accuracy. 

 Eric9Points 21 May 2020
In reply to ianstevens:

Yes, I should have said reliable rather than accurate.

In reply to neilh:

> What exactly is the point? Great you have had it. Are you immune....err based on the science there is no proof you are immune.

> What are you going to do with the results???

> Please emlighten me what is the benefit to you of getting the test done.

I think I'd like to know if I have detectable antibodies (although I'd like to know some details of how the test works and what sort of antibodies it's claiming to detect).  I would be prepared to assume that a strongly positive test is likely to give me at least partial protection at least for, say, 12 months.  Whether I'm prepared to spend £200 without a lot more information, though, probably not. 

By partial protection I mean a reduced risk of developing severe disease and, perhaps, an increased resistance to developing symptoms from a low viral dose.

What a weakly positive test would tell me is less clear.  I think I'd also want a PCR test to exclude being an asymptomatic carrier in that case. 

 neilh 21 May 2020
In reply to Dave Garnett:

The manufacturer of the Antibody test kits- Abbot- has said they are not intended for  home use.

Do not buy, they are a waste of time.

I do not understand all this -will it might work-- you might as well buy Trumps drug of choice hydroxychloroquine as well.

Post edited at 13:56
In reply to Eric9Points:

Seeing as post infection immunity is questionable, what is actually the point, apart from finding out if you've had it or not?
And, according to The Sun, at £69 a pop, forget it!

1
 Red Rover 21 May 2020
In reply to Taylor's Landlord:

There is good news on that front, it looks like infection and recovery do give immunity. Many people have tested positive for Covid-19 weeks after recovery but it turns out that this was just fragments of SARS-CoV-2 RNA still in the body. The fragments can't do any harm but they do trigger a test into giving a positive result.

This is based on a study by the south korean centre for disease control. I don't think it's translated into English yet but there is a discussion of it here by a nurse on youtube.

https://www.youtube.com/watch?v=uATMbGK__Tg&t=1s

Also sources here :

http://m.koreaherald.com/view.php?ud=20200429000724

https://www.livescience.com/coronavirus-reinfections-were-false-positives.html

https://www.independent.co.uk/news/world/asia/coronavirus-south-korea-patients-infected-twice-test-a9491986.html

Post edited at 15:20
 mullermn 21 May 2020
In reply to Red Rover:

I saw in the news today that a study on monkeys had shown immunity as well.

If it does make you immune then there’s a danger it’s going to trigger a weird arms race to get Covid and get recovered from it so that you can go back to normal life (good luck persuading people who know they’re immune to sit at home just for the benefit of those who aren’t).

I wonder if employers will be allowed to ask for test results so that they can have ‘Covid safe’ teams working at full efficiency. Could create a weird two class society, and some proper moral dilemmas. Do you deliberately get infected knowing that there’s no reliable treatment and it could kill you, or do you sit at home not being able to work and wait to lose your shirt through loss of income?

 Red Rover 21 May 2020
In reply to mullermn:

I don't know the answer to that but in any case these problems are much less serious than the problems we would face if infection and recovery didn't give immunity! It was always a frightening prospect.

 Eric9Points 21 May 2020
In reply to mullermn:

While knowledge that having immunity presents a number of issues, overall it is undeniably good news.

 mullermn 21 May 2020
In reply to Eric9Points:

Oh yeah, I don’t think there’s much question of that!

In reply to mullermn:

> If it does make you immune

I don't think there's much doubt that anyone who recovers from C19 has some degree of immunity.  If you don't develop an effective immune response you die. 

What doesn't necessarily follow is that an antibody test is an accurate reflection of that immune response (either because what killed off the virus was the T-cell response killing infected cells, or because the important part of the antibody response was a mucosal IgA response in the airways rather than being high IgG levels in the blood).

Also unclear is how long a protective response will last but I'm fairly optimistic about that.  As far as I know this virus doesn't integrate or have any latent life cycle, so the main problem would probably be antigenic variation - and so far it seems relatively stable.   

 Red Rover 21 May 2020
In reply to Dave Garnett:

There are viruses that you don't get immunity from after recovery. It's possible, but rare, for your immune system to be able to save your life but not respond any faster the second time round. I can only think of one case of that though. Either way it's good news that the Korean CDC have found that re-infection isn't happening. SARS-CoV-2 doesn't seem to mutate too quickly either. 

 tcashmore 21 May 2020
In reply to neilh:

> The manufacturer of the Antibody test kits- Abbot- has said they are not intended for  home use.

> Do not buy, they are a waste of time.

> I do not understand all this -will it might work-- you might as well buy Trumps drug of choice hydroxychloroquine as well.

On your last point, perhaps trump isn’t as mad as we all think - I see nhs is running a trial starting now!  Apart from the fact that if they thought it was any use, why has it taken until the 20th May to start,  I thought previous trials had shown it to be useless and dangerous?  Just shows, can’t trust anything at the moment. 

In reply to Red Rover:

>  I can only think of one case of that though.

Which were you thinking of?  I think dengue can be tricky and there's something called antibody-dependent enhancement that can actually make it easier for viruses to infect some types of cells (ones with Fc receptors) once they've been bound by antibody, but a true lack of any anamnestic reponse would be pretty unusual in an immunocompetent person. 

Anyway, the closest evidence we have must be from SARS-CoV-1, where there are demonstrable memory T-cells (but not antibodies or B cells) 6 years out I think.

Post edited at 18:10
 Red Rover 21 May 2020
In reply to Dave Garnett:

I was thinking of dengue but I may have misunderstood it. 

 neilh 21 May 2020
In reply to tcashmore:

Well there is loads of drugs etc being tried out as it is the path to gold and dollars.  

Does  not mean it works though. 
 

why do people think there is an instant cure out there? At the moment it just seems like wishful thinking. 

 tcashmore 21 May 2020
In reply to neilh:

You misunderstand my post, apologies. I don’t think there is an instant cure out there, I’m more surprised that the NHS are now just starting a trial on this now - do they have more information that has come to light to make it worthwhile -  It seemed to me that this malarial drug had come and gone as an option

 Eric9Points 23 May 2020
In reply to Eric9Points:

A bit more on where we are with anti body testing from a reporter who tested positive with three different tests .

https://www.bbc.co.uk/news/health-52762939

 toad 23 May 2020
In reply to Eric9Points:

That's really interesting. He still doesn't seem convinced he had it

 krikoman 23 May 2020
In reply to MargieB:

> If you have had Covid 19 intensely , get over it, are later exposed and have minor symptoms, is that the body building long term immunity? I presume one is still infectious with minor symptoms and should isolate, but over time, with  perhaps further exposure, enough immunity is built in the body? I'm not a doctor but is someone medically minded on this one?


It's probably the opposite, you might well be getting more and more damage to parts of your body, it's been found to hamper kidney function, and has been associated with some brain lesions, and lung damage, amongst other damage it can do.

There was a good Horizon program about it earlier this week.

I some people there is a huge anti-body response, in others next to none.

1
 krikoman 23 May 2020
In reply to Eric9Points:

> Somewhere on Twitter.

Really, is Twitter the best place for this sort of information?

> The point is that people don't get C19 twice.

Are you sure? there's not a lot of evidence that you can't, at present at least.

In reply to Eric9Points:

> I hear Superdrug are selling them. Even if they are not that accurate if I took three tests over three days and got the same result each time I'd have an accurate test, yes? <

On BBC TV this morning a guy said if that if one had three different tests (ie fingerprick type tests from different manufacturers) that were all positive then that is a reliable result. Sounds reasonable.

Post edited at 08:47
 Eric9Points 24 May 2020
In reply to krikoman:

> Really, is Twitter the best place for this sort of information?

> Are you sure? there's not a lot of evidence that you can't, at present at least.

The Tweet was from an expert and was one of those multi tweet things which went on for several hundred words. Can't remember what the guy was exactly but a professor of something relevant. I always check profiles of people I intend to take seriously.

 off-duty 24 May 2020
In reply to krikoman:

> Really, is Twitter the best place for this sort of information?

> Are you sure? there's not a lot of evidence that you can't, at present at least.

The evidence appears to show that there aren't any cases of people catching it twice. Those cases that appear to have suggested double infections have mostly been explained, either by false negative/positive tests or shedding of "dead" viral particles.

That isn't the same as evidence demonstrating immunity but it's far more positive than if there were cases of double infection popping up all over the place.

In addition the virus seems to be showing a very low mutation rate - unlike the common cold/flu, so in principle immunity should be possible.

 Toccata 24 May 2020
 HardenClimber 24 May 2020
In reply to Eric9Points:

Accuracy: Is the answer right

Precision: How close are the values recorded (high precision does not mean high accuracy) (think about target shooting and having a tight cluster, but wide of the centre) (Sometimes called repeatability)

Reproducibility: How close values are when a test is used in different contexts (different marksman)(sometimes seen as a subset of precision).

(sometimes poor precision can be compensated for by using multiple values, to produce a more precise answer by 'averaging' , but that result may still be inaccurate ) (ie the average of your 20 shots could be anywhere on the target, it might give an accurate result, but it is important to see that the set are regarded as one test when assessing accuracy, and the number of tests is pre-determined)

Not sure what 'reliable' means when thinking about tests.

> Yes, I should have said reliable rather than accurate.

 elsewhere 24 May 2020
In reply to HardenClimber:

Reliability - false positives and false negatives.

A postive Covid test is unlikely to be a false positive. 

A negative Covid test is less reliable with more false negatives.

Theres seems to be an issue that some people don't have much of the virus in throat/nose swabs. 

People with mild symptoms might have mild antibody response which doesn't get picked up by antibody test. 

Is it just the nature of how a particular  individual reacts to the virus that some (milder?) cases are difficult to detect?

In reply to elsewhere:

It's quite an intrusive test I believe, you have to shove the swab to the back of the throat until you gag and up your nose until quite often it draws blood. I'm not sure I would do that to myself very successfully.


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