Author: Dr Mark Ali MBBS BSc FRCS CTh, Medical Director
Positive antibody result
The blood sample you have given shows that you have IgG antibodies to SARS-CoV-2 (the covid-19 virus). This means that you can be highly confident that you have been infected by covid-19 and developed antibodies to it.
How accurate are the results?
Sensitivity concerns the false negative rate and is expressed as a percentage. The antibody test has a sensitivity of 100% when tested at least 14 days after your first symptoms. Put another way, 14 days after symptom onset, every person infected by covid-19 and developed antibodies is identified as positive by this test (there are no false negatives).
Specificity concerns the false positive rate and is expressed as a percentage. The Covid-19 antibody test has a 99.63% specificity. This means that out of every 10,000 people tested, 37 (0.37%) will be incorrectly identified as having antibodies to covid-19 when they do not (false positive).
Note that the antibody tests were developed for use and have been validated on venous blood samples (blood taken from a vein by a medical professional) rather than samples of blood taken from a fingerprick. This may affect the accuracy of the test. This is why we recommend having a medical professional take your blood sample, which can be done at home or in the clinic.
Does this mean you are immune?
Scientists do not know yet. In general, IgG antibodies to a particular virus usually confer some immunity and protection from reinfection. However, we do not know if this is the case for covid-19. Previous studies on related coronaviruses show that IgG antibodies to these viruses give some form of immunity, at least in the short term. For covid-19, if these antibodies are protective, we do not know how long this immunity will last.
It is therefore crucial that you continue to follow all relevant government guidance related to social distancing and measures against contracting or spreading covid-19. Please follow the latest most up-to-date government advice, which can be found here: https://www.nhs.uk/conditions/coronavirus-covid-19/. If you need further advice, feel short of breath or have concerns you are not coping with the illness, please contact 111.
Negative antibody result
The blood sample you have given shows that you have no IgG antibodies to SARS-CoV-2 (the covid-19 virus). This means that it is very unlikely that you have been infected by covid-19 and produced antibodies.
If you would like to discuss your results further or have any concerns, please contact the clinic at: +44 (0)20 3916 5990.