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I have had a negative antibody test despite being unwell with symptoms of Covid-19 – how should I interpret this?



Advice from a Consultant in Infectious Diseases

This information is sourced from Dr Sarah Logan, Consultant in Infectious Diseases and General Medicine

Q.  I have had a negative antibody test despite being unwell with symptoms of Covid-19 over 2 months ago. I have heard several colleagues have also unexpectedly tested negative, some of whom had Covid-19 confirmed on antigen testing at the time of illness. How should we interpret this, given that we have been told the antibody tests have very high specificity and sensitivity?

A.

The main tests in UK labs are the Roche and Abbott platforms which at present are both measuring IgG to the N protein on the surface of the virus

The tests are validated but we are all ( including the immunologists) learning a lot about this virus and our host response as we treat and meet more and more patients with a spectrum of illness

There are many reasons an antibody test may be negative

  1. It was not Covid-19
  2. It was Covid-19 but it was a while ago and the amount of detectable IgG has decreased
  3. It was Covid-19 but the patient did not mount an IgG response because perhaps their mucosal immunity was so effective that they did not mount a response detectable in the blood. Lots of research is trying to address this

SO if the test is positive- this means the patient has antibodies, it does not tell us if they are protected from future exposure, it does confirm they had Covid-19 but a negative serological result does not tell us they did not have Covid-19

There are some useful links below

Sources

Published: 30/06/2020
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