These are tests that detect the presence in the serum (a part of the blood) of antibodies (Immunoglobulins, Ig) produced by the immune system to defend itself from what comes from outside (Antigens), and that can be a threat, such as SARS-CoV-2 and therefore indicate whether or not a subject has come into contact with an infectious agent.
The quantitative serological test with CLIA method is done through a venous sampling from the arm performed by a nurse and a subsequent laboratory analysis of the blood tube with CLIA method carried out at the authorized laboratory of the MultiMedica Group: the Polo Scientifico Tecnologico of Milan. These tests, in addition to detecting the presence of IgM and IgG antibodies, also measure the amount of IgG.
The antibodies called “IgM” are produced in the initial phase of the infection, are found in the blood from 3 to 6 days after the onset of symptoms and then tend to disappear within a few weeks. The other antibodies, called “IgG”, are produced later and are found in the blood starting from a couple of weeks after the onset of symptoms (but may appear even earlier) and should then remain for a long time.
The serological test can therefore provide the following results:
- IgM and IgG negative: there has been no infection, or exposure to the pathogen occurred too recently and no detectable immune reaction has yet developed, or the level of antibodies produced is too low to be detected by the test;
- only IgM positive: exposure to the antigen is very recent.
- IgM and IgG positive: the infection is ongoing and has been contracted recently;
- Only IgG positive: the infection has been there but is not recent.
To whom is the IgG test addressed?
- Those who want to verify if they have been in contact with the virus in the past and therefore have already developed neutralizing antibodies.
- Those who have already completed the SARS – CoV-2 vaccine (both doses) and want to verify the subsequent production of antibodies (and their relative duration, through repeated measurements over time).
Depending on the results, other tests may be needed to arrive at an accurate diagnosis.