Acronyms define the antibodies produced to defend the body from foreign organisms
To aid in the diagnosis of COVID-19 pictures, some tests were developed by the laboratories as a way to identify the presence of the new coronavirus in the body. Among them are serology tests, which detect IgG and IgM antibodies.
According to José Geraldo Leite Ribeiro, an epidemiologist at the Pardini Group, the results of these tests appear only as positive, negative or indeterminate. It is the physician who assesses whether the case is worrying or not, based on the patient’s clinical condition and history.
However, before the pandemic, these antibody tests were already used in diagnostic medicine to screen the population’s immunity against some diseases, such as zika, dengue and chikungunya. Therefore, understand below what these tests really indicate and what negative and positive results mean.
What is IgG and IgM
IgG and IgM are classes of antibodies (defense molecules), produced by the body specifically against a certain antigen – a foreign substance to the body, which can be a virus, bacteria or toxin. IgM antibodies appear in the acute phase of infection, whereas IgG tend to appear a little later.
In fact, there are 5 different types of these? Proteins? defenders of the body, which are: IgA, IgM, IgE, IgG and IgD. Of these, the most analyzed in exams are IgE, IgM and IgG. While IgE has a greater association with allergies, the presence of positive IgM and IgG tends to indicate the body’s exposure to an infectious agent, either in a late or early stage.
The tests that analyze the presence of these antibodies are called serology tests. In practice, they are performed by collecting a small blood sample and presenting the result in minutes.
In general, when the results of the IgM and IgG tests appear positive, the indication is that the person had contact with the antigen and then started producing antibodies against it.
A negative result, on the other hand, is due to the fact that the test was carried out when there was still no production of antibodies in the body – which does not mean that the person does not have a virus.
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Non-infection is a possibility, but so was the test before the immune response. Therefore, it is important to combine the test result with a medical evaluation.
Therefore, in the case of COVID-19, for example, the test cannot be used to confirm that someone has the disease or not, since the person can carry the virus, but has not yet developed an immune response with the production. of IgM and IgG.
As for the reliability of the tests, it is necessary to check the specificity and sensitivity of the exam being performed. When going to the preferred laboratory, the client has the right to question the effectiveness of the exam.
Here are the possible combinations of results for the test and what they may indicate:
What does non-reactive IgG and reactive IgM mean?
Probably, the person is at the beginning of the disease – which is when we have, in general, positive IgM (reagent), characteristic of the acute phase of the disease, and negative IgG (non-reactive), which is usually produced a little later.
What does IgG reagent and IgM reagent mean?
About 10 days after the onset of the disease, the two classes of immunoglobulin (IgM and IgG) are usually positive. That is, the person has already produced both the antibody that appears faster (IgM), and the one that appears a little later (IgG). Usually, at this stage, the person no longer has so many symptoms of the disease.
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What does non-reactive IgG and non-reactive IgM mean?
When IgM and IgG are non-reactive after 10 days of illness, the person was probably not infected by the tested antigen. If she has had symptoms, it could mean infection by another agent. But this is only confirmed with medical monitoring, as the tests can be false-negative in about 10% of patients.
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