Immunoglobulin M (IgM), which is found mainly in the blood and lymph fluid, is the first antibody to be made by the body to fight a new infection (the acute phase). IgM can be tested and detected very early after infection and disappears within 1 to 2 months after the infection (see the graph below).
Immunoglobulin G (IgG), the most abundant type of antibody, is found in all body fluids and protects against for example bacterial and viral infections. IgG is the antibody being produced from the middle -, and through the infection period all the way into the late stage infection (see the graph below). It is also this immunoglobulin-type which will be synthesized as a response to a new infection with SARS-CoV-2 and try to destroy the infection process. Therefore, a positive result for IgG indicates that the patient is either recovering or has had a previous infection.