Serology and Infectious Diseases

Serology is related to the analytical study of blood serum . In practical terms, the main objective of the serology test is to identify the presence of antigens belonging to various microorganisms and antibodies that are developed in response to the presence of these infectious agents in the patient’s blood. Through this procedure it is possible to identify diseases such as syphilis, dengue, herpes, HIV, hepatitis, toxoplasmosis and several others.


Antibodies or immunoglobulins are produced by the immune system. Each antibody is unique, created for a specific type of microorganism. They are proteins that protect people against microscopic invaders such as viruses, bacteria, chemicals and toxins. Each antibody produced recognizes a specific structure of an invasive cell or particle. The specific recognized structure is called an antigen. Antibodies bind to antigens, creating antigen-antibody complexes (immune complexes), which serve as a signal for the destruction of the antigen by the immune system.

The first time someone is exposed to an infectious agent, the immune system takes some time to recognize the antigens involved and produce enough specific antibodies to fight infection. The initial response is formed by IgM antibodies. Some time later, production of IgG antibodies begins. The body “remembers” and maintains a small stock of antibodies so that the next time it is exposed to the same microorganism, the organism responds with more intensity and speed, providing protection mainly through IgG antibodies.

The immune system can also identify a part of our body as foreign and produce autoantibodies against it. These autoantibodies cause an inflammatory reaction that causes damage to the tissues involved. An autoimmune response can affect a single organ or be systemic, affecting tissues or organs. These reactions cause autoimmune disorders or autoimmune diseases.

Antibodies can also elicit immune responses to blood transfusions and organ transplants. For this reason, donor / recipient compatibility tests are essential so that the blood or organs match as much as possible and minimize the likelihood of an immune response, rejection in the case of organs and TRALI in the case of blood.


Immunoglobulins are produced by plasmocytes, widely found through the serology technique in blood, tissue fluid and exocrine fluid, representing about 20% of the total plasma protein. There are five different classes of immunoglobulins (IgM, IgG, IgE, IgA and IgD). The three immunoglobulins most frequently investigated in tests are IgM, IgG and IgE. IgM and IgG antibodies have a joint action in the immediate and long-term protection against infections.

Immuno globulin A ( IgA ) It is found in high concentrations in mucous membranes, particularly those lining the airways and gastrointestinal tract, as well as in saliva and tears.
Immunoglobulin G ( IgG ) It is the most abundant type of antibody, found in all body fluids and protects against bacterial and viral infections.
Immunoglobulin M ( IgM ) Found mainly in the blood and lymphatic fluid, it is the first antibody to be produced by the body to fight a new infection.
Immunoglobulin E ( IgE ) It is mainly associated with allergic reactions (when the immune system reacts excessively to environmental antigens, such as pollen or animal hair). It is found in the lungs, skin and mucous membranes.
Immunoglobulin D ( IgD ) It exists in small amounts in the blood, it is the least understood antibody.


This application of serology is traditionally used to diagnose pathologies, right at the initial stages. Thus, the doctor is able to indicate the most appropriate treatment, increasing the chances of cure and alleviating the symptoms. In addition to being an indirect way of acting in the fight against contagion. The serum analysis is made from a patient’s blood sample.

When a new infection occurs, the first antibodies produced are the IgM that decrease as the infection is controlled, giving rise to the IgG, which remains for the rest of life.

Positive IgM and

Negative IgG

Indicates recent infection.
Negative IgM and

Positive IgG

It indicates that the patient has had the disease for a long time, has healed and is now immunized, without the risk of having it again.
Negative IgM and

Negative IgG

It suggests that the patient is not sick and has no immunity against the infection, and may contract it if exposed.

There is not really a “normal” concentration of antibody, as people produce them in different amounts. Patients with weakened immune systems may not be able to respond normally, producing less antibodies or responding more slowly to antigenic exposure. The detailed significance of an antibody test result depends on the patient’s symptoms and the specific circumstances that led to the test.


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