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New Abbott SARS-CoV-2 antibody test has 99.90% specificity and 100% sensitivity

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Re: New Abbott SARS-CoV-2 antibody test has 99.90% specificity and 100% sensitivity

#81

Post by concordDance »

jrockway wrote: post #68
cerebral_oasis wrote: post #38

I took this antibody test through LabCorp on Friday and tested positive. I have been in strict (see: paranoid) isolation with one other person since March 7 and haven't felt sick or anything close to it since then. I did have what I thought was a strange flu/cold early February with a sore throat, post-nasal drip, wildly varying body temperature, and lower back pains. In hindsight those are COVID-19 symptoms. the per…

Good anecdote. I also had a "weird cold" in February with symptoms that are unusual for me but typical of COVID-19, and have been waiting to get the antibody test. I kind of expect it to turn out the same way. (Otherwise, I would really like to figure out what the "weird cold" that everyone had in February was. Because it sure was weird, and everyone I know had it.)

Yet Another Weird February Cold with COVID-19 symptoms checking in.

Re: New Abbott SARS-CoV-2 antibody test has 99.90% specificity and 100% sensitivity

#82

Post by madhadron »

ghshephard wrote: post #47
barbegal wrote: post #22

> We tested 1,020 serum specimens collected prior to SARS-CoV-2 circulation in the United States and found one false positive This gives 95% confidence intervals of between 0.0% and 0.5% false positive rate.

Okay - I'm going to reveal my statistics ignorance here - but if they did get a false positive, how does 0.0% fall within the range of possibilities (or is that allowing for it might be 0.0499..% or lower?)

We know that 0% isn't a real value for a test's error rate, but the statistical procedure being used doesn't have any "look, it's never zero" criteria built into its math. All it says is that 0 is one of the numbers consistent with the data given these criteria.

Re: New Abbott SARS-CoV-2 antibody test has 99.90% specificity and 100% sensitivity

#83

Post by jrockway »

y-c-o-m-b wrote: post #75
jrockway wrote: post #68

Earlier quoted context omitted.

Good anecdote. I also had a "weird cold" in February with symptoms that are unusual for me but typical of COVID-19, and have been waiting to get the antibody test. I kind of expect it to turn out the same way. (Otherwise, I would really like to figure out what the "weird cold" that everyone had in February was. Because it sure was weird, and everyone I know had it.)

"Weird cold" in February checking in. I did not have any temperature variations or fevers, but I got struck with a fatigue like no other. For the first time since I was 3 years old, I took afternoon naps three days in a row because I was just completely wiped out. It's rare for me to take a nap at all (happens maybe once a year)! It took two weeks to get out of this fatigued state. My other symptoms were "chills-like…

I agree with you on being open to thinking that COVID-19 arrived earlier than was initially thought. When I first shared my "weird cold" story on HN, the consensus was that I was a crazy person and there was no way that could be COVID-19. There would be more deaths if it had been here. But now there are some deaths, and a large number of people with "weird cold" stories, and it really makes me think that a lot of people have already had this. Maybe the doctors at the time didn't recognize it as COVID-19 (I didn't when I had my weird cold). Maybe the numbers that we see now are just wrong; i.e. the recorded cases we have are just the tip of the iceberg (and if you tested everyone every week, we would have hundreds of millions of cases).

Or maybe that weird cold was just a weird cold and nothing more. It seems unlikely to me, but I'm open to it. I hate to make public policy suggestions on anecdotes... but someone should really look into that weird cold. Everyone in New York had it. It sure is weird.

Re: New Abbott SARS-CoV-2 antibody test has 99.90% specificity and 100% sensitivity

#84

Post by iso1631 »

mlyle wrote: post #30
pgcudahy wrote: post #6

There seems to be no analysis of whether these are neutralizing antibodies. The idea of using serology for immunity certificates or "golden tickets" is never going to go well. Even with 99.9% specificity, if the population prevalence is 1%, 10% of positives will be false positives. If in real world testing, specificity is 99% and population prevalence is 1%, then 50% of positives are false positives.

> if the population prevalence is 1% But the population prevalence is much more than 1%: 80k deaths at a 1% infection fatality rate (and I believe this is high, but I'm being conservative) implies 8,000,000 infections so far. This is more like 2.5%. So far. 95% CI for specificity is 99.5%, so you can be reasonably confident that you're doing better than 85%. It may not be a perfect intervention, but you could really…

> I disagree with it for other reasons (it incents people to go get sick to be free/be able to work/etc).

On an individual basis yes, but doign large scale scientifically/statistically relevant antibody tests to see just how many people have actually had covid-19, would be very beneficial.

Re: New Abbott SARS-CoV-2 antibody test has 99.90% specificity and 100% sensitivity

#85

Post by djaque »

cerebral_oasis wrote: post #38

I took this antibody test through LabCorp on Friday and tested positive. I have been in strict (see: paranoid) isolation with one other person since March 7 and haven't felt sick or anything close to it since then. I did have what I thought was a strange flu/cold early February with a sore throat, post-nasal drip, wildly varying body temperature, and lower back pains. In hindsight those are COVID-19 symptoms. the per…

Yeah, I'm pretty sure I had it and didn't have bad symptons back in Feb. too. Just a light sore throat and generally feeling gross. It'll be interesting to see how many people really caught it once this is all over.

Re: New Abbott SARS-CoV-2 antibody test has 99.90% specificity and 100% sensitivity

#86

Post by ssully »

jrockway wrote: post #68
cerebral_oasis wrote: post #38

I took this antibody test through LabCorp on Friday and tested positive. I have been in strict (see: paranoid) isolation with one other person since March 7 and haven't felt sick or anything close to it since then. I did have what I thought was a strange flu/cold early February with a sore throat, post-nasal drip, wildly varying body temperature, and lower back pains. In hindsight those are COVID-19 symptoms. the per…

Good anecdote. I also had a "weird cold" in February with symptoms that are unusual for me but typical of COVID-19, and have been waiting to get the antibody test. I kind of expect it to turn out the same way. (Otherwise, I would really like to figure out what the "weird cold" that everyone had in February was. Because it sure was weird, and everyone I know had it.)

I had something weird in March. It was a mix of a mild burning feeling in my chest, loss of appetite, and fatigue. I honestly thought it was just anxiety related to the quarantine manifesting in symptoms, and it very well might have been, but I have no idea.

Re: New Abbott SARS-CoV-2 antibody test has 99.90% specificity and 100% sensitivity

#87

Post by gwd »

InvaderFizz wrote: post #49
gwd wrote: post #23

Earlier quoted context omitted.

Let me give it a try. Suppose we have 100,000 people in a statistically representative town. If 1% of people have had COVID-19, then that's 1000 people who have had it, and 99,000 people who haven't. The test has a sensitivity of 100%, which means all 1000 people who've had it will test positive. The test has a specificity of 99.9%, which means 98,901 of the 99,000 people who haven't had it will test negative; but th…

So if I'm understanding this correctly, with this test. If you test negative, you are clear, guaranteed, no false negatives. If you test positive, there is a 10% chance it's a false positive. I guess my follow up question, does a retest of the positive population make that false positive rate drop to 0.1%, or is the reason for false positive significant to an individual and not random chance?

> If you test positive, there is a 10% chance it's a false positive.

Well, don't misunderstand -- it's got nothing to do with the test per se, but with the probability that you had the disease in the first place.

The test itself has two probabilities:

1. If you've had COVID-19, the probability that it will report positive (sensitivity)

2. If you haven't had COVID-19, the probability that it will report negative (selectivity)

But those probabilities give you a mapping from reality -> test_result. What you want is the reverse of that -- and find the probability from a test_result -> reality. When you do that, you have to factor in the probability that you have the disease in the first place.

If 50% of the population have had COVID-19, then a positive test means a 99.9% probability of having had the virus. If 1% of the population, a positive test means 91% likely you have it. If only 1 in a million people had COVID-19, then the number of false positives would completely overwhelm the number of true positives.

This is sometimes called the "Base rate fallacy": forgetting to factor in the base rate when determining something like this.

It's important for things like, say, systems which automatically detect terrorists at airports. How many travelers at an airport are actually terrorists planning to attack a plane? It's got to be one in hundreds of millions, if not billions. With that low of a base rate, even if you had a system that was 99.999% accurate, the vast majority of people it flagged up would be innocent.

Re: New Abbott SARS-CoV-2 antibody test has 99.90% specificity and 100% sensitivity

#88

Post by jointpdf »

InvaderFizz wrote: post #49
gwd wrote: post #23

Earlier quoted context omitted.

Let me give it a try. Suppose we have 100,000 people in a statistically representative town. If 1% of people have had COVID-19, then that's 1000 people who have had it, and 99,000 people who haven't. The test has a sensitivity of 100%, which means all 1000 people who've had it will test positive. The test has a specificity of 99.9%, which means 98,901 of the 99,000 people who haven't had it will test negative; but th…

So if I'm understanding this correctly, with this test. If you test negative, you are clear, guaranteed, no false negatives. If you test positive, there is a 10% chance it's a false positive. I guess my follow up question, does a retest of the positive population make that false positive rate drop to 0.1%, or is the reason for false positive significant to an individual and not random chance?

I had the same question about retesting. Here’s a quote from Scott Gottlieb (former FDA commissioner):

“While all of these tests can still generate false positives—a finding that you have the antibodies when you don’t—that risk can be sharply reduced by repeating the test if it comes back positive. The predictive value of two consecutive positive tests is high enough that you can be confident antibodies are present.”

https://www.wsj.com/articles/antibody-knowledge-can-be-power...

Re: New Abbott SARS-CoV-2 antibody test has 99.90% specificity and 100% sensitivity

#89

Post by thoraway1010 »

cerebral_oasis wrote: post #38

I took this antibody test through LabCorp on Friday and tested positive. I have been in strict (see: paranoid) isolation with one other person since March 7 and haven't felt sick or anything close to it since then. I did have what I thought was a strange flu/cold early February with a sore throat, post-nasal drip, wildly varying body temperature, and lower back pains. In hindsight those are COVID-19 symptoms. the per…

The results I got had a big FDA warning that positive results may be a result of other infections (ie, that the tests are not specific to covid).

I feel like the WHO (body may not produce antibodies as part of beating covid, antibodies have not been shown to confer any immunity) and now the FDA may be talking about true but theoretical issues.

What is the REAL rate, in the USA, of folks who have for example MERS antibodies that will trigger a false positive in this type of test. Ie, do these tests really come back positive for MERS antibodies and how likely am I to have had MERS but not covid so that I get that false positive?

Given the FDA warning (which was the biggest thing on my results) I'm guessing 30%+ of positives are a result of these situations? But interested in actual data

Re: New Abbott SARS-CoV-2 antibody test has 99.90% specificity and 100% sensitivity

#90

Post by GabeIsman »

jrockway wrote: post #68
cerebral_oasis wrote: post #38

I took this antibody test through LabCorp on Friday and tested positive. I have been in strict (see: paranoid) isolation with one other person since March 7 and haven't felt sick or anything close to it since then. I did have what I thought was a strange flu/cold early February with a sore throat, post-nasal drip, wildly varying body temperature, and lower back pains. In hindsight those are COVID-19 symptoms. the per…

Good anecdote. I also had a "weird cold" in February with symptoms that are unusual for me but typical of COVID-19, and have been waiting to get the antibody test. I kind of expect it to turn out the same way. (Otherwise, I would really like to figure out what the "weird cold" that everyone had in February was. Because it sure was weird, and everyone I know had it.)

Another New Yorker with a weird cold at the end of February here!
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