Author: Dr Mark Ali MBBS BSc FRCS CTh, Medical Director
I want to know if I have covid-19, should I take the antibody test?
If you think you currently have covid-19, please ensure that you stay at home and that you and your household follow government guidelines to self-isolate.
To test if you currently have covid-19, we would recommend the antigen test performed by PCR on a swab sample taken from the nose and throat. This will tell you if there is virus present right now.
The antibody test is different . It shows whether you have had a Covid-19 infection, - even one with no symptoms - in the past. It detects IgG antibodies to covid-19. If positive, it indicates that you have been infected by covid-19 and produced a measurable immune response.
The test is most accurate from 14 days after the first day of symptoms (to ensure enough time has passed to produce the antibodies in measurable levels). It is possible to have antibodies present and a positive PCR test (i.e. to have developed an immune response but still have detectable virus).
A lot of companies are selling home sampling kits for the antibody test. Why aren't you providing this service?
We do recognise the convenience of a home sampling test. This is why we offer both at home and in-clinic testing by a medical professional. However, the manufacturer has stressed that the test has only been validated on blood samples taken from a vein. We want to assure the accuracy of the test and so will only offer the test via venipuncture (from the vein) until validation studies show that the results are equitable to those obtained from capillary blood (fingerprick test).
I felt ill a couple of months ago and wonder if this might have been covid-19, could I take the antibody test?
The covid-19 antibody test will detect IgG antibodies to covid-19, showing an immune response to covid-19. The antibody test is very sensitive and specific if taken after 14 days from the start of symptoms.
Some studies have reported that some people have had covid-19 but do not have a detectable antibody response. It may be that a different part of the immune system has cleared the virus. These are small studies and we need to know more.
I haven’t had any symptoms but have been around people who have, can I take the antibody test?
It depends on when your last contact was and how significant the contact was. If you have had significant contact with symptomatic people recently, please ensure that you follow government guidelines to self-isolate.
It can take up to 14 days from when someone is infected to display symptoms (incubation period) and another 14 days after that to develop antibodies. An antibody test may show an immune response but we recommend waiting a month to do this from your significant contact and to follow stay at home advice as above.
Can I visit my loved ones who are vulnerable if I get a positive antibody test?
It is incredibly tough at the moment to have such reduced social contact. However, in order to protect our loved ones, it is vital that we continue to follow government advice. We do not know for certain if antibodies protect against infection and how long this protection lasts. Furthermore, you could still carry the virus on clothing, packaging etc. It is a heavily researched area and we eagerly await further updated guidance as the evidence accumulates.
How accurate are the antibody tests?
The antibody tests are very accurate if taken at least 14 days following the onset of symptoms. The antibody test has been approved by Public Health England. It has a sensitivity of 100% and a specificity of 99.63%.