7 ms·

PCR tests don't detect antibodies, they detect active virus. Antibody tests may be what you're thinking of. See: https://www.fda.gov/consumers/consumer-updates

PCR tests don't detect antibodies, they detect active virus. Antibody tests may be what you're thinking of. See: https://www.fda.gov/consumers/consumer-updates/coronavirus-disease-2019-testing-basics https://www.fda.gov/consumers/consumer-updates/coronavirus-d... I don't know the answer to your question, but it would make sense unless the antibody test(s) look for a specific type of antibody to COVID-19 that is produced naturally when infected and not just any antibodies that might be produced when vaccinated.

toolz 5y ago
incorrect, PCR tests detect any virus matter - active or otherwise. This is a very important distinction since we've seem to lost our minds collectively and label PCR tests with a cycle threshold of >40 as a true positive.
- mlyle 5y ago
  "lost our minds collectively" -- no, made a sane tradeoff in the sensitivity vs. specificity ratio when the disease is common. It's not like the sensitivity is wonderful even with a large number of PCR cycles, and the false positive rate was not too bad. As the disease becomes less common, it makes sense to turn down the sensitivity of the test. Base rate fallacy, yada yada.
  - toolz 5y ago
    here's a study showing above CT 32 not a single live virus was able to be cultured [1] - if this study accurately portrays reality then there's nothing resembling sanity with PCR CTs >40 https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciaa1579/5937368 https://academic.oup.com/cid/advance-article/doi/10.1093/cid... (image from the study) https://i.imgur.com/AaZZIXM.png https://i.imgur.com/AaZZIXM.png
    - mlyle 5y ago
      People who are infected will not necessarily have a single live virus in a swab you collect. Yes, if you can't culture it, they probably are not infectious right now but that is a different distinction. You're also putting a whole lot of weight on a study with what, about 50 total positives? And of them, very few with a Ct of over 35.
      - toolz 5y ago
        do you know of a study that shows the opposite? Because I know of more studies that have similar findings. here's one I found with a quick google (haven't read the study) https://pubs.acs.org/doi/10.1021/acsomega.1c00166 https://pubs.acs.org/doi/10.1021/acsomega.1c00166
        mlyle 5y ago
        Even your studies show a relatively low false positive rate with high numbers of cycles, and it's hoped that it increases sensitivity. No, we have no perfect data, because we have no perfect "infection test". High sensitivity was very worthwhile early in the pandemic, when infection was common and the predictive value of a test with a somewhat higher false positive rate was still high. Now that COVID is becoming rarer, we should absolutely be reducing cycle counts. The target should be to keep >75% of positives with actual infection even as the underlying rate of the disease decreases. I think we've exceeded this threshold by a large margin thus far. If you have a cogent statistical argument that disagrees instead of handwaving about cycle counts, I'm willing to listen.
        toolz 5y ago
        1st study says zero active virus beyond CT>32 and 2nd study shows 34ct is the cutoff for infectivity and that 2nd study also cites a 3rd study that ct>35 decreased to 8% active viruses All of those numbers are below 40ct - if this doesn't convince you that 40ct is the wrong number I don't know what to say - you've provided zero evidence that 40ct is beneficial and try to downplay extremely high false positives shown in three studies when you go to 40ct

toolz 5y ago

incorrect, PCR tests detect any virus matter - active or otherwise. This is a very important distinction since we've seem to lost our minds collectively and label PCR tests with a cycle threshold of >40 as a true positive.

mlyle 5y ago
"lost our minds collectively" -- no, made a sane tradeoff in the sensitivity vs. specificity ratio when the disease is common. It's not like the sensitivity is wonderful even with a large number of PCR cycles, and the false positive rate was not too bad. As the disease becomes less common, it makes sense to turn down the sensitivity of the test. Base rate fallacy, yada yada.
- toolz 5y ago
  here's a study showing above CT 32 not a single live virus was able to be cultured [1] - if this study accurately portrays reality then there's nothing resembling sanity with PCR CTs >40 https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciaa1579/5937368 https://academic.oup.com/cid/advance-article/doi/10.1093/cid... (image from the study) https://i.imgur.com/AaZZIXM.png https://i.imgur.com/AaZZIXM.png
  - mlyle 5y ago
    People who are infected will not necessarily have a single live virus in a swab you collect. Yes, if you can't culture it, they probably are not infectious right now but that is a different distinction. You're also putting a whole lot of weight on a study with what, about 50 total positives? And of them, very few with a Ct of over 35.
    - toolz 5y ago
      do you know of a study that shows the opposite? Because I know of more studies that have similar findings. here's one I found with a quick google (haven't read the study) https://pubs.acs.org/doi/10.1021/acsomega.1c00166 https://pubs.acs.org/doi/10.1021/acsomega.1c00166
      - mlyle 5y ago
        Even your studies show a relatively low false positive rate with high numbers of cycles, and it's hoped that it increases sensitivity. No, we have no perfect data, because we have no perfect "infection test". High sensitivity was very worthwhile early in the pandemic, when infection was common and the predictive value of a test with a somewhat higher false positive rate was still high. Now that COVID is becoming rarer, we should absolutely be reducing cycle counts. The target should be to keep >75% of positives with actual infection even as the underlying rate of the disease decreases. I think we've exceeded this threshold by a large margin thus far. If you have a cogent statistical argument that disagrees instead of handwaving about cycle counts, I'm willing to listen.
        toolz 5y ago
        1st study says zero active virus beyond CT>32 and 2nd study shows 34ct is the cutoff for infectivity and that 2nd study also cites a 3rd study that ct>35 decreased to 8% active viruses All of those numbers are below 40ct - if this doesn't convince you that 40ct is the wrong number I don't know what to say - you've provided zero evidence that 40ct is beneficial and try to downplay extremely high false positives shown in three studies when you go to 40ct