Serology tests made on blood samples are used to detect virus-specific IgM and/or IgG-class antibodies that are produced in the body while infected. The presence of virus-specific IgG in the blood may indicate that the person was infected with the virus but not necessarily that the person is ill or carries or spreads the virus now. It is a simple test, which allows for the results to be obtained in a few hours. Limitations of these tests: insufficient accuracy, as antibodies being present in the blood does not necessarily indicate the presence of the virus.
IgM antibodies develop within a week and IgG antibodies within 2-3 weeks of the contraction of the infection.
at the onset of the disease, the person may falsely test negative.
Serology tests can give false negative results if there has not been enough time for SARS-CoV-2 specific antibodies to develop at the time of the test, or false positives under particular pathologies when large amounts of different specific antibodies are present in the sample.