Tests for the novel coronavirus disease-2019 (COVID-19) include the diagnostic polymerase chain reaction (PCR) test (using respiratory samples, such as nasal swabs) or the antibody test (using blood from either finger prick or taking blood from your vein). A diagnostic PCR test reveals that you are having an active infection, while an antibody test tells whether you had a past infection. Testing for COVID-19 is vital for individuals with symptoms consistent with COVID-19 such as fever, cough, or difficulty breathing or individuals who had close contact with a confirmed case whether they have symptoms or not, to control transmission and to determine the resolution of infection. You should always consult an online doctor before getting such tests done.
Antibody tests (or sometimes called serology tests) checks your blood for antibodies which shows that you had a past infection from the virus causing COVID-19. Antibodies immunoglobulin M (IgM), which develops early in an infection, and immunoglobulin G (IgG), which develops after you have recovered, are proteins that fights off the infection and usually provide immunity against getting the same disease again. The incubation period for the novel coronavirus is around 5 to 7 days and up to 14 days. Depending on the timing of the antibody test done from the time when a person gets infected, it may not be positive in a current COVID-19 infection, hence it is not used to diagnose an active infection with COVID-19. However, it should be done in those with COVID-19 symptoms but the COVID-19 PCR test is not available for immediate access. The antibody test is also useful if you are asymptomatic and experienced a COVID-19-like illness or if there were exposure to confirmed cases in the prior 14 days.
The Food and Drug Administration (FDA) has authorized some antibody tests for this virus but these tests are not 100% accurate and false-positive or false-negative results may occur. If you test positive on a COVID-19 antibody test, it shows that you have antibodies from an infection with the virus that causes COVID-19, or it may be a related virus from the same family (called coronavirus) such as ones that causes the common cold. You may also test positive for antibodies if you had an asymptomatic infection, which is an infection without symptoms of COVID-19. It is not known yet if someone who recovers from COVID-19 or develops antibodies can get reinfected again and how long this protection might last. If you test negative on a COVID-19 antibody test, you could still have a current infection ongoing as antibodies typically take 1 to 3 weeks after infection to develop, or some people may not develop antibodies at all. This means that you could still get sick if there is recent exposure to the virus and you could still spread the virus.
Regardless of whether you test positive or negative on a COVID-19 antibody test, the results do not confirm if you have a current infection, if you can spread the virus or if you are immune to reinfection of COVID-19, hence steps to protect oneself such as social distancing and use of mask should be continued until further information are available. If you have symptoms of COVID-19 after the antibody tests or had close contact with a confirmed case, you should have a COVID-19 PCR test done to detect current infection. An antibody test cannot determine if you are currently having COVID-19.
Based on the current available information, the WHO does not recommend the use of antibody tests as a diagnostic test for patients but it should be used to support the research on the development of vaccines and the further understanding of the disease.