COVID IgG SEROLOGY
Wellington SCL has introduced IgG serological testing for COVID-19. It is a tier 2 test, with funded testing only available after approval from a specialist in Infectious Diseases, Infection Control or Public Health. Other requests will incur a fee of $100.25 inc GST.
From 2nd November you will be able to request the COVID-19 IgG test via eclair eordering. The electronic order form includes mandatory clinical information relating to timing and type of exposure and type of symptoms.
Antibody testing is most useful to see whether someone has been infected with COVID-19 two weeks to several months previously. It would be most useful for those who think they may have developed COVID-19, but could not get tested at the time.
Serology does not have a useful role for diagnosing acute infection, because it takes up to 14 days to develop antibodies, and IgM antibodies do not appear much sooner than IgG. PCR remains the mainstay of acute diagnosis and contact tracing. It appears that some people, particularly those with mild disease, do not develop antibodies or lose them after several weeks.
We have several methods available which detect antibodies to nucleocapsid (N) protein or spike (S) protein. Because of a small risk of false positive results, any positive result will be confirmed with a second test before issuing positive results. Positive results should be discussed with the medical officer of health.
We do not have enough experience with COVID-19 serology to understand how long antibodies persist and how well they correlate with immunity from reinfection. This is because they are not a direct measure of neutralising antibodies, which means they are not recognised for generating an “immune passport”. On the basis of small studies conducted overseas, it does seem likely that those with detectable antibodies will be immune, at least for the duration of detectable antibodies, but this is not guaranteed.