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Covid-19 Primary Care Resources

When to take an antigen or antibody test for Covid-19

After a few days of illness the concentration of the virus falls

This information is sourced from the UK Research and Innovation Website (UKRI):

Testing during the course of infection

  • The test for the virus detects the genetic material (nucleic acid) of the virus during an active infection. It is also called a PCR test or nucleic acid test
  • The coronavirus can be detected in swabs taken from the nose or throat, even before symptoms of illness first appear
  • The nucleic acid test is most reliable and can be used in the first 7 days of illness
  • The test might be unreliable between days 7-10
  • Some people have no symptoms throughout their infection but are positive on the virus test and infectious to others

The antibody test (blood test):

  • Will only detect infections after the immune system has produced antibodies that recognise the virus
  • This happens approximately 7–10 days after symptoms develop
  • There is a clear link between the presence of the antibody and protective immunity for many common viral infections
  • This link has not yet been confirmed for the new coronavirus
  •  It is possible that people are temporarily protected against reinfection but that the protection wanes with time


Published: 14/04/2020