A Negative to both IgM & IgG results means that this test was not able to detect any antibody that may have been produced. It is possible however that the patient could have been infected and have mounted an immune response that was not detectable by this test - either because the infection was mild and did not lead to the production of a detectable amount of antibody, because the antibodies produced bind a different virus protein to the one used in this test, or because the antibody levels have not yet risen to a detectable level. Repeat testing in 2 week’s time or longer following a negative result may lead to a positive result if this scenario is a possibility. It is also of course possible that COVID-19 infection has not occurred.
Increasingly it is being suggested that some individuals with a positive Covid 19 PCR (diagnostic swab) test result may never mount an antibody response that is detectable by antibody testing, and that the response in these individuals may be stronger via the immune system’s T cells; or alternatively that antibodies are produced, but for some only for a relatively brief period of time and that the level of antibody may then decline therefore becoming undetectable after a few months.