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[[File:Blood in tubes (9617266704).jpg|right|250px]]Blood serum or serology assays come in three common varieties: LFA, enzyme-linked immunosorbent assay (ELISA), or neutralization assay.<ref name="JHSerology20">{{cite web |url=https://www.centerforhealthsecurity.org/covid-19TestingToolkit/serology/Serology-based-tests-for-COVID-19.html |title=Serology tests for COVID-19 |author=Center for Health Security |publisher=Johns Hopkins University |date=26 August 2021 |accessdate=06 September 2021}}</ref> As discussed prior, LFAs are intended to be rapid point-of-care tools for qualitatively testing body fluids for patient antibodies or viral antigen. The ELISA is, in contrast, a more lab-bound method which produces results that are qualitative or quantitative. In the context of COVID-19 testing, ELISA tests for the presence of patient antibodies in a given specimen based upon whether or not an interaction is observed with the viral proteins present on the test plate. However, even if antibodies are present, ELISA isn't able to tell a clinician if those antibodies are able to protect against future infection. Neutralization assays are the lengthiest to complete, taking from three upwards to five days.<ref name="JHSerology20" /> This is largely due to the fact that the assay depends on culturing cells that encourage growth of the target virus. Afterwards, introduced patient antibodies, if present, will fight to prevent viral infection of cells. This process is performed in decreasing concentrations, giving the clinician an opportunity to "visualize and quantify how many antibodies in the patient serum are able to block virus replication."<ref name="JHSerology20" /> In contrast to ELISA, a neutralization assay is able to determine if a patient's antibodies are actively fighting against the target virus, even after recovering from the infection. In November 2020, the FDA granted an EUA to the first ELISA-based serology test to detect nuetralizing antibodies from recent or prior SARS-CoV-2 infection.<ref name="FDACoronaNeut20">{{cite web |url=https://www.fda.gov/news-events/press-announcements/coronavirus-covid-19-update-fda-authorizes-first-test-detects-neutralizing-antibodies-recent-or |title=Coronavirus (COVID-19) Update: FDA Authorizes First Test that Detects Neutralizing Antibodies from Recent or Prior SARS-CoV-2 Infection |author=Food and Drug Administration |publisher=Food and Drug Administration |date=06 November 2020 |accessdate=18 November 2020}}</ref>
An antigen is a substance—often a protein but may also be an environmental like a virus—that provokes the immune system to produce an antibody against it.<ref name="MPAntigen">{{cite web |url=https://medlineplus.gov/ency/article/002224.htm |title=Antigen |work=MedlinePlus |publisher=U.S. National Library of Medicine |accessdate=07 August 2020}}</ref> As such, another approach to testing for the presence of a virus in a specimen is to test for the antigen rather than the antibody. An antigen test is useful as a repeated surveillance test, but it has drawbacks as a one-time diagnostic test.<ref name="Anderson5Invest20">{{cite web |url=https://www.wcvb.com/article/5-investigates-concerns-about-current-use-of-rapid-antigen-tests-for-covid-19/33538332 |title=5 Investigates: Concerns about current use of rapid antigen tests for COVID-19 |author=Anderson, K. |work=WCVB 5 ABC |date=06 August 2020 |accessdate=07 August 2020}}</ref><ref name="ServiceRadical2020">{{cite journal |title=Radical shift in COVID-19 testing needed to reopen schools and businesses, researchers say |journal=Science |author=Service, R.F. |year=2020 |doi=10.1126/science.abe1546}}</ref><ref name="KremerUWSys20">{{cite web |url=https://urbanmilwaukee.com/2020/08/07/uw-system-orders-350000-covid-19-tests/ |title=UW System Orders 350,000 COVID-19 Tests |author=Kremer, R. |work=Urban Milwaukee |date=07 August 2020 |accessdate=07 August 2020}}</ref> For COVID-19 and other viral infections, an antigen test has the advantage that specimen collection can typically be done with a simple nasal swab rather than a more invasive [[nasopharyngeal swab]]. Another advantage, on one hand, is that antigen testing is more rapid and convenient because the extraction and amplification steps of PCR are not used. On the other, antigen testing is less sensitive for the same reason: you test only what's there (rather than amplifying the amount for greater sensitivity).<ref name="ServiceRadical2020" /><ref name="GuglielmiTheExp20">{{cite journal |title=The explosion of new coronavirus tests that could help to end the pandemic |journal=Nature |author=Guglielmi, G. |volume=583 |pages=506–09 |year=2020 |doi=10.1038/d41586-020-02140-8}}</ref>


Johns Hopkins' Center for Health Security [https://www.centerforhealthsecurity.org/covid-19TestingToolkit/serology/Serology-based-tests-for-COVID-19.html appears to be tracking] serology-based COVID-19 tests that are in development or have been approved in various parts of the globe. However, for the most up-to-date list of serology tests that have received EUAs in the United States, the FDA's [https://www.fda.gov/medical-devices/coronavirus-disease-2019-covid-19-emergency-use-authorizations-medical-devices/in-vitro-diagnostics-euas-serology-and-other-adaptive-immune-response-tests-sars-cov-2 EUA list] appears to be the best source. As of September 2021, the FDA shows 88 serology assays approved for diagnostic use in the U.S. Of those 88, sixteen are explicitly listed as being ELISA-based.
A theory increasingly gaining traction, however, is that "[a] higher frequency of testing makes up for poor sensitivity.”<ref name="ServiceRadical2020" /><ref name="KremerUWSys20" /><ref name="ClarkCOVID20">{{cite web |url=https://www.medpagetoday.com/infectiousdisease/covid19/87930 |title=COVID Antigen Tests: Coming to Case Counts Near You? |author=Clark, C. |work=MedPage Today |date=06 August 2020 |accessdate=07 August 2020}}</ref> Several researchers have shared pre-print and published research suggesting this outcome<ref name="ServiceRadical2020" />:


A review of Johns Hopkins' tracking list showed more LFA-based tests among those approved in other parts of the world. Among their list of those still in development, an LFA stands out for integrating CRISPR detection.<ref name="MBAProto20">{{cite web |url=https://mammoth.bio/wp-content/uploads/2020/03/Mammoth-Biosciences-A-protocol-for-rapid-detection-of-SARS-CoV-2-using-CRISPR-diagnostics-DETECTR.pdf |format=PDF |title=A protocol for rapid detection of the 2019 novel coronavirus SARS-CoV-2 using CRISPR diagnostics: SARS-CoV-2 DETECTR |publisher=Mammoth Biosciences |date=02 March 2020 |accessdate=09 April 2020}}</ref> CRISPR (clustered regularly interspaced short palindromic repeats) represents bacterial and archaeal DNA sequences derived from DNA fragments of previous infection. This genetic material can then be used as an activator of biomarkers when attached RNA "guides" find a match with target viral RNA in patient specimen.<ref name="NatureCRISPR18">{{cite web |url=https://www.nature.com/articles/d41586-018-02200-0 |title=CRISPR’s powers unleashed for disease detection |work=Nature - Research Highlights |date=16 February 2018 |accessdate=09 April 2020}}</ref> This CRISPR-based LFA, called DETECTR, was further described in a paper published in October 2020, with the authors concluding it could be used "as a complementary technically independent approach to qRT-PCR, thereby increasing the testing capacity of medical microbiological laboratories and relieving the existent PCR-platforms for routine non-SARS-CoV-2 diagnostic testing."<ref name="BrandsmaRapid20">{{cite journal |title=Rapid, sensitive and specific SARS coronavirus-2 detection: A multi-center comparison between standard qRT-PCR and CRISPR based DETECTR |journal=The Journal of Infectious Diseases |author=Brandsma, E.; Verhagen, H.J.M.P.; van de Laar, T.J.W. et al. |volume=In Print |at=jiaa641 |year=2020 |doi=10.1093/infdis/jiaa641 |pmid=33038252 |pmc=PMC7665660}}</ref>
<blockquote>Larremore and his colleagues have modeled the benefits of more frequent tests, even ones that are less accurate than today’s. Fast tests repeated every three days, with isolation of people who test positive, prevents 88% of viral transmission compared with no tests; a more sensitive test used every two weeks reduced viral transmission by about 40%, they report in a 27 June preprint on medRxiv. Paltiel and his colleagues reached much the same conclusion when they modeled a variety of testing regimes aimed at safely reopening a 5000-student university. In a 31 July paper in JAMA Network Open, they found that, with 10 students infected at the start of the semester, a test that identified only 70% of positive cases, given to every student every two days, could limit the number of infections to 28 by the end of the semester. Screening every seven days allowed greater viral spread, with the model predicting 108 infections.</blockquote>
 
As such, the utility of antigen testing, despite its lower sensitivity, appears to be surveillance situations where a large group of individuals who are at risk can be screened at regularly scheduled intervals of two to four days. The end result, in theory, would be few people who are target-positive would be missed, positives could be isolated and verified with a more sensitive test, and more target-positive people would be identified and isolated before reaching peak infectivity.<ref name="ServiceRadical2020" /><ref name="CourageCovid20">{{cite web |url=https://www.vox.com/2020/7/31/21336212/covid-19-test-results-delays |title=Should we be testing fewer people to stop the spread of Covid-19? |author=Courage, K.H. |work=Vox |date=31 July 2020 |accessdate=05 August 2020}}</ref> To be clear, it's not a perfect solution, but as Harvard epidemiologist Michael Mina and Boston University economist Laurence Kotlikoff suggest, "[w]e need the best means of detecting and containing the virus, not a perfect test no one can use."<ref name="CourageCovid20" /> In August 2020, a coalition of six U.S. state governors bought into that concept and agreed to work together with the Rockefeller Foundation, as well as the Quidel Corporation and Becton, Dickinson and Company, which had received FDA EUAs to market antigen tests for SARS-CoV-2.<ref name="ClarkCOVID20" /><ref name="MervoshItsLike20">{{cite web |url=https://www.nytimes.com/2020/08/04/us/virus-testing-delays.html |title=‘It’s Like Having No Testing’: Coronavirus Test Results Are Still Delayed |author=Mervosh, S.; Fernandez, M. |work=The New York Times |date=04 August 2020 |accessdate=05 August 2020}}</ref> As of September 2021, thirty-four FDA EUAs for antigen tests have been issues; 28 of those 34 include allowances for CLIA-waived testing, and 10 were authorized for home use.<ref name="FDAInVitroAntigen21">{{cite web |url=https://www.fda.gov/medical-devices/coronavirus-disease-2019-covid-19-emergency-use-authorizations-medical-devices/in-vitro-diagnostics-euas-antigen-diagnostic-tests-sars-cov-2 |title=In Vitro Diagnostics EUAs - Antigen Diagnostic Tests for SARS-CoV-2 |publisher=U.S. Food and Drug Administration |date=07 September 2021 |accessdate=07 September 2021}}</ref>


==References==
==References==
{{Reflist|colwidth=30em}}
{{Reflist|colwidth=30em}}

Revision as of 18:33, 3 February 2022

An antigen is a substance—often a protein but may also be an environmental like a virus—that provokes the immune system to produce an antibody against it.[1] As such, another approach to testing for the presence of a virus in a specimen is to test for the antigen rather than the antibody. An antigen test is useful as a repeated surveillance test, but it has drawbacks as a one-time diagnostic test.[2][3][4] For COVID-19 and other viral infections, an antigen test has the advantage that specimen collection can typically be done with a simple nasal swab rather than a more invasive nasopharyngeal swab. Another advantage, on one hand, is that antigen testing is more rapid and convenient because the extraction and amplification steps of PCR are not used. On the other, antigen testing is less sensitive for the same reason: you test only what's there (rather than amplifying the amount for greater sensitivity).[3][5]

A theory increasingly gaining traction, however, is that "[a] higher frequency of testing makes up for poor sensitivity.”[3][4][6] Several researchers have shared pre-print and published research suggesting this outcome[3]:

Larremore and his colleagues have modeled the benefits of more frequent tests, even ones that are less accurate than today’s. Fast tests repeated every three days, with isolation of people who test positive, prevents 88% of viral transmission compared with no tests; a more sensitive test used every two weeks reduced viral transmission by about 40%, they report in a 27 June preprint on medRxiv. Paltiel and his colleagues reached much the same conclusion when they modeled a variety of testing regimes aimed at safely reopening a 5000-student university. In a 31 July paper in JAMA Network Open, they found that, with 10 students infected at the start of the semester, a test that identified only 70% of positive cases, given to every student every two days, could limit the number of infections to 28 by the end of the semester. Screening every seven days allowed greater viral spread, with the model predicting 108 infections.

As such, the utility of antigen testing, despite its lower sensitivity, appears to be surveillance situations where a large group of individuals who are at risk can be screened at regularly scheduled intervals of two to four days. The end result, in theory, would be few people who are target-positive would be missed, positives could be isolated and verified with a more sensitive test, and more target-positive people would be identified and isolated before reaching peak infectivity.[3][7] To be clear, it's not a perfect solution, but as Harvard epidemiologist Michael Mina and Boston University economist Laurence Kotlikoff suggest, "[w]e need the best means of detecting and containing the virus, not a perfect test no one can use."[7] In August 2020, a coalition of six U.S. state governors bought into that concept and agreed to work together with the Rockefeller Foundation, as well as the Quidel Corporation and Becton, Dickinson and Company, which had received FDA EUAs to market antigen tests for SARS-CoV-2.[6][8] As of September 2021, thirty-four FDA EUAs for antigen tests have been issues; 28 of those 34 include allowances for CLIA-waived testing, and 10 were authorized for home use.[9]

References

  1. ↑ "Antigen". MedlinePlus. U.S. National Library of Medicine. https://medlineplus.gov/ency/article/002224.htm. Retrieved 07 August 2020. 
  2. ↑ Anderson, K. (6 August 2020). "5 Investigates: Concerns about current use of rapid antigen tests for COVID-19". WCVB 5 ABC. https://www.wcvb.com/article/5-investigates-concerns-about-current-use-of-rapid-antigen-tests-for-covid-19/33538332. Retrieved 07 August 2020. 
  3. ↑ 3.0 3.1 3.2 3.3 3.4 Service, R.F. (2020). "Radical shift in COVID-19 testing needed to reopen schools and businesses, researchers say". Science. doi:10.1126/science.abe1546. 
  4. ↑ 4.0 4.1 Kremer, R. (7 August 2020). "UW System Orders 350,000 COVID-19 Tests". Urban Milwaukee. https://urbanmilwaukee.com/2020/08/07/uw-system-orders-350000-covid-19-tests/. Retrieved 07 August 2020. 
  5. ↑ Guglielmi, G. (2020). "The explosion of new coronavirus tests that could help to end the pandemic". Nature 583: 506–09. doi:10.1038/d41586-020-02140-8. 
  6. ↑ 6.0 6.1 Clark, C. (6 August 2020). "COVID Antigen Tests: Coming to Case Counts Near You?". MedPage Today. https://www.medpagetoday.com/infectiousdisease/covid19/87930. Retrieved 07 August 2020. 
  7. ↑ 7.0 7.1 Courage, K.H. (31 July 2020). "Should we be testing fewer people to stop the spread of Covid-19?". Vox. https://www.vox.com/2020/7/31/21336212/covid-19-test-results-delays. Retrieved 05 August 2020. 
  8. ↑ Mervosh, S.; Fernandez, M. (4 August 2020). "‘It’s Like Having No Testing’: Coronavirus Test Results Are Still Delayed". The New York Times. https://www.nytimes.com/2020/08/04/us/virus-testing-delays.html. Retrieved 05 August 2020. 
  9. ↑ "In Vitro Diagnostics EUAs - Antigen Diagnostic Tests for SARS-CoV-2". U.S. Food and Drug Administration. 7 September 2021. https://www.fda.gov/medical-devices/coronavirus-disease-2019-covid-19-emergency-use-authorizations-medical-devices/in-vitro-diagnostics-euas-antigen-diagnostic-tests-sars-cov-2. Retrieved 07 September 2021. 
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