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17 april 2020

The Promise and Peril of Antibody Testing for COVID-19 - JAMA

The Promise and Peril of Antibody Testing for COVID-19 - JAMA

17-4-2020; doi:10.1001/jama.2020.6170
By: Jennifer Abbasi

Aim: Describe the value of antibody screening

Keys:

  • Antibody tests are useful for epidemiologic purposes and promising for return-to-society screening. However, further research is needed. 
  • Antibody tests cannot be used for diagnosis of COVID-19 in ill patients. PCR should still be used. 

Summary:

  • Antibody tests are, unlike PCR, not intended to identify active SARS-CoV-2. It detects IgM and IgG in the blood which, for most people, show up after over a week of symptoms when symptoms may already be waning.

     

    • It can confirm suspected cases in a late stage
    • It can reveal who was infected and didn’t know (asymptomatic spreaders)
  • Implications for the health care workforce could be substantial; reinfection is very unlikely when serological immunity is shown. 
  • Antibody tests might be critical in: disease surveillance, therapeutics, return-to-work screenings. 
  • Serology tests are used to screen donor blood for antibodies. Plasma containing antibodies is then transfused to gravely ill patients in an experimental treatment known as convalescent plasma. Early results are promising.

     

    • However; investigators question if patients receiving convalescent plasma gain remaining immunity.
  • The antibody concentration can be measured by ELISA and is important information, the higher the titer the more protected. 

     

    • Cheaper, lateral flow assays, can not measure quantitative information. 

       

      • Many of these have not been tested and validated. They should not be used to diagnose or exclude infection!

         

        • Not only do serologic tests miss contagious cases with early symptoms. It also misses infections in patients unable to make immunoglobulines (E.g. immunocompromised patients)
  • For the reasons above, PCR should remain gold standard. Antibody tests in acute setting could have serious public health consequences. 
  • It can be used for epidemiological purposes and for return-to work of critical (immune) workers. E.g. immuno nursing home nurses will not get COVID-19 again and infect patients. 

     

    • However; allowing people to reenter society based on their antibody status assumes that past infection guards against reinfection, something that researchers said was likely but not yet well defined.
    • In addition, is the virus not still active at time of antibody test? Are carriers not still contagious?!