4 ms·

You may have misheard the MD. The current tests have a very low false positive rate. That means if the test says you have Coronavirus, you have it. There's no "

by fma 7y ago

You may have misheard the MD. The current tests have a very low false positive rate. That means if the test says you have Coronavirus, you have it. There's no "burden". Where the tests are "not very accurate" is the false negative. The false negative rate can be as high as 50-60%, depending on tests and how it's administered. Sometimes they will conduct the test twice to improve accuracy. The Roche ones recently approved have a lower negative test rate (10%?) Edit: I removed my mention of 0% false positive rate because nothing in life is absolute.

whatshisface 7y ago
A 0% false positive rate is not possible. What if they switch your sample with someone else's while it's being handled by a human? Edit: >That means if the test says you have Coronavirus, you have it. This line implies the parent comment is talking about the false positive rate of the entire testing process that results in you being told you're infected, not PCR as a platonic ideal, theoretical process.
- irishsultan 7y ago
  That's still not a false positive rate of the test. But I agree that 0% false positive rates are going to be nearly impossible to achieve (for just about anything that isn't mathematics).
  - deleted 7y ago
    [deleted]
- joking 7y ago
  That’s a protocol fault and has nothing to do with the accuracy of the test
- fma 7y ago
  From the FDA itself. Note how firm they are in regards to a positive, vs how cautious they are in regards to a negative. If you have COVID-19 RNA in your body...you have the virus. What does it mean if the specimen tests positive for the virus that causes COVID-19? A positive test result for COVID-19 indicates that RNA from SARS-CoV-2 was detected, and the patient is infected with the virus and presumed to be contagious What does it mean if the specimen tests negative for the virus that causes COVID-19? A negative test result for this test means that SARSCoV-2 RNA was not present in the specimen above the limit of detection. However, a negative result does not rule out COVID-19 and should not be used as the sole basis for treatment or patient management decisions. A negative result does not exclude the possibility of COVID-19. https://www.fda.gov/media/135662/download https://www.fda.gov/media/135662/download
  - deleted 7y ago
    [deleted]
  - rectang 7y ago
    > A positive test result for COVID-19 indicates that RNA from SARS-CoV-2 was detected, and the patient is infected with the virus You still haven't addressed the possibility of a protocol error such as a switched sample. The lab test itself may never produce false positives, but that emphatically does not mean that if the lab test comes back positive there is a 100% guarantee that the patient is infected.
    - fma 7y ago
      Considering the context that I replied to is "we should also be aware of the danger of false positives", I think given the FDA source I posted (and what I've read elsewhere) I can say that there is absolutely no need to be aware of a danger of false positives in terms of disrupting people's lives. If you want to argue on the fact of life that nothing in life is absolute. Fine. you win. If administered properly, and the test kit detects a presence of COHVID-19 RNA in your body, and the person telling you the results is not drunk, then the results is as close as 0% as practical.
- kylebenzle 7y ago
  Don't you know you get downvoted here on HN for telling the truth. These idiots like to think they've got it all figured out. Of course there is no such thing as a 0% false positive test.
andrewla 7y ago
> The current tests have a 0% false positive rate. Need a citation on this. In order to even make a strong statement about the false positive rate you need to have some sort of alternate confirmation mechanism, usually clinical diagnosis or another more comprehensive test. That kind of work takes time and we haven't gotten to the point where we know this. False positives in the test are one possible reason for the resurgence in Singapore; the initial screenings were overreporting the number of cases leading to a false sense of security, followed by a surge in real cases as the spread continued. EDIT: A quick look at some of the tests available indicate that currently providers are not publishing specificity/sensitivity numbers in general under the accelerated release guidelines. One I did find was biomedomics test [1], which claims "The overall testing sensitivity was 88.66% and specificity was 90.63%", so ~10% of negative cases will show as positive. [1] https://www.biomedomics.com/products/infectious-disease/covid-19-rt/ https://www.biomedomics.com/products/infectious-disease/covi...
- makomk 7y ago
  That's an antibody-based test not approved for diagnostic use in the US, which is faster but less accurate than the RT-PCR ones currently being used.
  - andrewla 7y ago
    It's just the only one that I could get numbers on. So... show me sensitivity/specificity numbers that show a 0% false positive rate. The CDC PCR test [1], for example, has some data and no false positives, but the sample sizes are so small (107 known negatives tested) that the best we can estimate is ~96% specificity. [1] https://www.fda.gov/media/134922/download https://www.fda.gov/media/134922/download
timhigins 7y ago
"Clinical characteristics of 24 asymptomatic infections with COVID-19 screened among close contacts in Nanjing, China." - https://link.springer.com/content/pdf/10.1007/s11427-020-1661-4.pdf https://link.springer.com/content/pdf/10.1007/s11427-020-166.... It seems asymptomatic patients can test negative multiple times on RT-PCR assays but be diagnosed other ways. I've read somewhere that at least in China, the specificity of the PCR tests is only 60-70%, leaving ~30% undetected. From the Discussion section of this paper: https://pubs.rsna.org/doi/10.1148/radiol.2020200642 https://pubs.rsna.org/doi/10.1148/radiol.2020200642: "According to current diagnostic criterion, viral nucleic acid test by RT-PCR assay plays a vital role in determining hospitalization and isolation for individual patients. However, its lack of sensitivity, insufficient stability, and relatively long processing time were detrimental to the control of the disease epidemic. In our study, the positive rate of RT-PCR assay for throat swab samples was 59% (95%CI, 56%-62%) which was consistent with previous report (30 - 60%) (6). In addition, a number of any external factors may affect RT-PCR testing results including sampling operations, specimens source (upper or lower respiratory tract), sampling timing (different period of the disease development) (6), and performance of detection kits. As such, the results of RT-PCR tests must be cautiously interpreted."

by fma 7y ago

whatshisface 7y ago

A 0% false positive rate is not possible. What if they switch your sample with someone else's while it's being handled by a human? Edit: >That means if the test says you have Coronavirus, you have it. This line implies the parent comment is talking about the false positive rate of the entire testing process that results in you being told you're infected, not PCR as a platonic ideal, theoretical process.

irishsultan 7y ago
That's still not a false positive rate of the test. But I agree that 0% false positive rates are going to be nearly impossible to achieve (for just about anything that isn't mathematics).
- deleted 7y ago
  [deleted]
joking 7y ago
That’s a protocol fault and has nothing to do with the accuracy of the test
fma 7y ago
From the FDA itself. Note how firm they are in regards to a positive, vs how cautious they are in regards to a negative. If you have COVID-19 RNA in your body...you have the virus. What does it mean if the specimen tests positive for the virus that causes COVID-19? A positive test result for COVID-19 indicates that RNA from SARS-CoV-2 was detected, and the patient is infected with the virus and presumed to be contagious What does it mean if the specimen tests negative for the virus that causes COVID-19? A negative test result for this test means that SARSCoV-2 RNA was not present in the specimen above the limit of detection. However, a negative result does not rule out COVID-19 and should not be used as the sole basis for treatment or patient management decisions. A negative result does not exclude the possibility of COVID-19. https://www.fda.gov/media/135662/download https://www.fda.gov/media/135662/download
- deleted 7y ago
  [deleted]
- rectang 7y ago
  > A positive test result for COVID-19 indicates that RNA from SARS-CoV-2 was detected, and the patient is infected with the virus You still haven't addressed the possibility of a protocol error such as a switched sample. The lab test itself may never produce false positives, but that emphatically does not mean that if the lab test comes back positive there is a 100% guarantee that the patient is infected.
  - fma 7y ago
    Considering the context that I replied to is "we should also be aware of the danger of false positives", I think given the FDA source I posted (and what I've read elsewhere) I can say that there is absolutely no need to be aware of a danger of false positives in terms of disrupting people's lives. If you want to argue on the fact of life that nothing in life is absolute. Fine. you win. If administered properly, and the test kit detects a presence of COHVID-19 RNA in your body, and the person telling you the results is not drunk, then the results is as close as 0% as practical.
kylebenzle 7y ago
Don't you know you get downvoted here on HN for telling the truth. These idiots like to think they've got it all figured out. Of course there is no such thing as a 0% false positive test.

andrewla 7y ago

> The current tests have a 0% false positive rate. Need a citation on this. In order to even make a strong statement about the false positive rate you need to have some sort of alternate confirmation mechanism, usually clinical diagnosis or another more comprehensive test. That kind of work takes time and we haven't gotten to the point where we know this. False positives in the test are one possible reason for the resurgence in Singapore; the initial screenings were overreporting the number of cases leading to a false sense of security, followed by a surge in real cases as the spread continued. EDIT: A quick look at some of the tests available indicate that currently providers are not publishing specificity/sensitivity numbers in general under the accelerated release guidelines. One I did find was biomedomics test [1], which claims "The overall testing sensitivity was 88.66% and specificity was 90.63%", so ~10% of negative cases will show as positive. [1] https://www.biomedomics.com/products/infectious-disease/covid-19-rt/ https://www.biomedomics.com/products/infectious-disease/covi...

makomk 7y ago
That's an antibody-based test not approved for diagnostic use in the US, which is faster but less accurate than the RT-PCR ones currently being used.
- andrewla 7y ago
  It's just the only one that I could get numbers on. So... show me sensitivity/specificity numbers that show a 0% false positive rate. The CDC PCR test [1], for example, has some data and no false positives, but the sample sizes are so small (107 known negatives tested) that the best we can estimate is ~96% specificity. [1] https://www.fda.gov/media/134922/download https://www.fda.gov/media/134922/download

timhigins 7y ago

"Clinical characteristics of 24 asymptomatic infections with COVID-19 screened among close contacts in Nanjing, China." - https://link.springer.com/content/pdf/10.1007/s11427-020-1661-4.pdf https://link.springer.com/content/pdf/10.1007/s11427-020-166.... It seems asymptomatic patients can test negative multiple times on RT-PCR assays but be diagnosed other ways. I've read somewhere that at least in China, the specificity of the PCR tests is only 60-70%, leaving ~30% undetected. From the Discussion section of this paper: https://pubs.rsna.org/doi/10.1148/radiol.2020200642 https://pubs.rsna.org/doi/10.1148/radiol.2020200642: "According to current diagnostic criterion, viral nucleic acid test by RT-PCR assay plays a vital role in determining hospitalization and isolation for individual patients. However, its lack of sensitivity, insufficient stability, and relatively long processing time were detrimental to the control of the disease epidemic. In our study, the positive rate of RT-PCR assay for throat swab samples was 59% (95%CI, 56%-62%) which was consistent with previous report (30 - 60%) (6). In addition, a number of any external factors may affect RT-PCR testing results including sampling operations, specimens source (upper or lower respiratory tract), sampling timing (different period of the disease development) (6), and performance of detection kits. As such, the results of RT-PCR tests must be cautiously interpreted."