Antibody testing in The Liverpool University Hospital Foundation Trust (LUHFT)
COVID-19 Antibody testing is a blood test to look whether somebody has produced an immune response (antibodies) to SARS-CoV2. It takes time for the immune system to produce this response. The time taken to produce antibodies varies between people from 5-7 days up to more than 6 weeks post infection. The test detects both IgG and IgM antibodies. However, a history of symptoms or confirmed COVID-19 by PCR at least 6 weeks ago makes current infection less likely.
A small number of people do not produce a detectable immune reaction even when they had confirmed COVID-19 by PCR. Reasons for this include i) illnesses or drugs which affect the immune system and ii) having mild COVID-19 symptoms.
Currently it is unknown whether immunity to SARS-CoV2 after infection develops and protects the individual against future infection and how long it lasts. It is therefore important to continue to follow Infection Prevention and Control Guidance regardless of the result of the antibody test.
A Positive Result:
A positive result means that it is very likely that the individual has been infected with SARS-CoV-2 virus in the last few weeks or months.
A Negative Result:
A negative result could mean one of the following:
that the individual has never been infected with SARS-CoV2 virus
that individual has been recently infected with SARS-CoV2 virus but the blood sample was tested too early to detect an immune response. Follow-up testing after 2 -4 weeks may be considered if necessary.
that the individual has been infected with SARS-CoV2 but the virus did not trigger a strong immune response.
Immunocompromised individuals may not be able to produce antibodies.
Antibody level may decline over time and eventually become negative.
We do not advise testing for antibodies to SARS-CoV-2 until at least 28 days post-symptom onset.
The sensitivity is 75% at 4 weeks after symptoms.
The specificity is 100%.
This data is derived from an internal verification.