Antigen Testing Debate As Approval Sought For Faster Coronavirus Testing

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Andrew Donaldson

Born and raised in West Virginia, Andrew has since lived and traveled around the world several times over. Though frequently writing about politics out of a sense of duty and love of country, most of the time he would prefer discussions on history, culture, occasionally nerding on aviation, and his amateur foodie tendencies. He can usually be found misspelling/misusing words on Twitter @four4thefire and his writing website Yonderandhome.com

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9 Responses

  1. fillyjonk fillyjonk
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    says:

    False negatives are gonna be a big problem with these. Because of the low protein levels in the samples. And this is one case where a false negative has more bad consequences than a false positive – false positive, the person gets sent home for a few days to ‘recover;’ false negative, the person could infect a bunch of people.

    Eventually we might get to an antibody/saliva test that’s GOOD but I don’t think we are there yet. I’ve seen reports of sensitivity rates in the 80 percents and that’s TERRIBLE because it will unleash people who can be spreading the disease on the rest of the world. This is why I’m leery about the “open everything up now” calls some are making

    (I always have to look up “sensitivity” vs. “specificity,” I am a biologist but not the medical kind; I think I used the correct term there – the one that detects true positives accurately – but it’s still early in the morning)Report

    • Avatar Oscar Gordon in reply to fillyjonk
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      says:

      It might not be ideal, but currently, we don’t have enough of the PCR tests, can’t make them fast enough to satisfy the demand, and thus you have lots of people running around infecting others anyway (because folks are breaking quarantine).

      The antigen tests at least increase the amount of knowledge we have, even if it’s not perfect.Report

    • Avatar PD Shaw in reply to fillyjonk
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      says:

      Seems like a 15 minute test would be wonderful to secure nursing homes or other high risk places. What Illinois has started doing is training staff to perform the swab test, and they have a contract with a lab to perform 3000 tests per day, with results in 48 hours. I’m not sure what test frequency that implies, weekly for a portion of those in the facility? Given how quickly the infection appears to spread inside these facilities, that type of testing seems to rely a lot on timing and luck.Report

  2. Avatar Brandon Berg
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    says:

    Because of the low protein levels in the samples. And this is one case where a false negative has more bad consequences than a false positive – false positive, the person gets sent home for a few days to ‘recover;’ false negative, the person could infect a bunch of people.

    How much does this matter? If there’s, say, a 5% false positive rate, is that enough to keep R_t above unity?

    For sensitivity and specificity, just think about the normal meanings of the words. Sensitivity is how sensitive a test is to detecting the disease; if it’s 90% sensitive, it will detect 90% of cases. Specificity is how specific positive results are to the disease; if it’s 98% specific, 98% of positive results will indicate an actual case.Report

    • Avatar veronica d in reply to Brandon Berg
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      says:

      It’s obviously useful as population screening. However, individuals will use the results to guide their behaviors, and the median member of the general public often doesn’t really understand probability that well. In other words, the risk is:

      “I tested negative” -> “It’s safe for me to visit grandma.”

      Ofc, public health officials can work to educate people, but how well does that work in general.

      Summary: false negatives do matter. They can cause harm.Report

  3. Avatar Kazzy
    Ignored
    says:

    The NYC metro area seems to have suddenly gotten access to widespread testing for both actively sick folks and those carrying antibodies. Because I had a high exposure risk (the boys’ mom contracted it and they were with her during her most contagious time and then with me for 16 days) but never contracted symptoms, I’ll be getting an antibody test later this week. It involves a blood draw and will get me “highly accurate results” within 3-5 days. I believe the active virus tests still involve the nasal swap. I can report back on the experience one it is complete.

    https://www.citymd.com/news/covid-19-testing-update?utm_source=sfmc&utm_medium=email&utm_campaign=4_27+COVID-19+Testing&utm_content=COVID-19+testing+FAQ

    This link is from CityMD, a major urgent care chain in the area. I spoke with my PCP whose office remains closed, but he can conduct a telehealth appointment to authorize a prescription for a test done at a lab. My sons’ pede can do the blood sample in office. This is all in Bergen County, NJ, one of the harder hit areas in the region.Report

  4. Avatar Brent F
    Ignored
    says:

    From my time in a biochem lab I’ll tell you that a good rule of thumb with a new antibody based test is to assume it’s overhyped junk until proven otherwise.

    Antibody-Antigen recognition is a chemically finicky thing that can be easily messed up by different conditions and frequently newly produced antibodies are as robust in recognition of their supposed target outside the manufacturers testing place. It isn’t nearly as robust and reliable of a biotechnology as PCR is.

    Until something like this had been demonstrated to work reliably as advertised in the field and not on the bench, be skeptical.Report

  5. Avatar Kazzy
    Ignored
    says:

    My results came back negative. Here is what was included with that:
    – Detection of IgG antibodies may indicate exposure to
    – SARS-CoV-2 (COVID-19). It usually takes at least 10 days
    – after symptom onset for IgG to reach detectable levels. An
    – IgG positive result may suggest an immune response to a
    – primary infection with SARS-CoV-2, but the relationship
    – between IgG positivity and immunity to SARS-CoV-2 has not
    – yet been firmly established. Antibody tests have not been
    – shown to definitively diagnose or exclude SARS-CoV-2
    – infection. Diagnosis of COVID-19 is made by detection of
    – SARS-CoV-2 RNA by molecular testing methods, consistent
    – with a patient’s clinical findings.

    – This test has not been reviewed by the FDA. Negative results
    – do not rule out SARS-CoV-2 infection particularly in those
    – who have been in contact with the virus. Follow-up testing
    – with a molecular diagnostic should be considered to rule
    – out infection in these individuals. Results from antibody
    – testing should not be used as the sole basis to diagnose
    – or exclude SARS-CoV-2 infection or to inform infection
    – status. Positive results could also be due to past or
    – present infection with non-SARS-CoV-2 coronavirus strains,
    – such as coronavirus HKU1, NL63, OC43, or 229E. This test
    – is not to be used for the screening of donated blood.Report

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