To detect immunoglobulin m (IgM)antibodies in an acute phase, blood should be collected 7 days after the onset of infection.
IgM and IgG antibodies to SARS-CoV-2 may both be found shortly after infection. IgG is typically detectable for extended periods of time, but IgM is most effective for diagnosing recent infection and typically becomes undetectable weeks to months after infection.
IgM antibody detection is frequently viewed as a sign of an acute infection. Due to cross-reactivity with IgM antibodies to other, closely related bacteria or other interfering chemicals, false-positive IgM findings are, nonetheless, frequently observed.
A positive IgM result may not always indicate an "acute" infection, and additional testing (such as IgG testing) may be required to interpret results because IgM antibodies may be detectable for 2-4 months (or longer) after disease resolution.
For many infections, the onset of a measurable antibody response is 5-7 days after the infection. If samples are taken before infection, the initial IgM test results may be negative. Antibody production Immunosuppressed patients may also continue to be seronegative.
