A positive IgG antibody test result suggests recent or prior infection with SARS-CoV-2. It usually takes at least 10 days after symptom onset for IgG detectable levels to be reached. Patients tested prior to this time may be negative for SARS-CoV-2 IgG antibodies. An IgG positive result may suggest an immune response to primary infection with SARS-CoV-2, but the relationship between IgG positivity and immunity to SARS-CoV-2 has not yet been firmly established. At this time, a positive IgG result has not been shown to indicate immunity, as such social distancing, also called “physical distancing,” should still be followed to assure that we continue to protect ourselves, our family, and our community.
A positive IgM and/or IgA test result, with a positive/negative IgG result, may indicate an active COVID-19 infection. A negative IgM and/or IgA antibody test result is likely to indicate that: (1) the person has not been infected with SARS-CoV-2 or (2) the person has been infected but there has not been enough time to produce an IgM and/or IgA response. Antibody tests have not been shown to definitively diagnose or exclude SARS-CoV-2 infection.
The presence of SARS-CoV-2 antibodies has been demonstrated in patients with undetectable viral RNA. Therefore, testing asymptomatic healthcare workers or patients with negative molecular diagnostic test results with antibody tests may add value in determining whether they have been exposed to SARS-CoV-2 or not.