Serology Definition
Serology Meaning: The clinical study of serum, as well as other bodily fluids, is known as serology. In practice, the term typically refers to the detection of antibodies in serum for diagnostic purposes. Antibodies are produced in response to infection (against a specific microorganism), such as foreign proteins (for instance, in response to a mismatched blood transfusion), or one's self-proteins.
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Serological Tests:
Serological tests involve diagnostic procedures for identifying antibodies and antigens in a patient's blood sample. Serology definition tells that Serological tests could be used to diagnose infections and autoimmune disorders, as well as to see whether a person is resistant to these kinds of diseases and for a variety of other purposes, including assessing a person's blood type.
The procedure for testing is simple. The majority of people do not experience extreme pain. Blood loss and infection are possible side effects, but the likelihood of either is poor.
In forensic serology, serological tests could be used to examine crime scene evidence. ELISA, complement-fixation, precipitation, agglutination, fluorescent antibodies, and, quite recently, chemiluminescence are all strategies for detecting antibodies and antigens.
Types of Serologic Tests:
Antibodies come in a variety of shapes and sizes. As a result, numerous tests exist to detect the existence of various forms of antibodies. There are some of them:
Antibodies exposed to specific antigens induce particle clumping in an agglutination assay.
By testing the presence of antibodies in body fluids, a precipitation test will determine if the antigens are identical.
The existence of antimicrobial antibodies in your blood is determined by their response to target antigens in the Western blot test.
Applications:
1. Microbiology:
Serologic tests have been used in microbiology to assess if an individual possesses antibodies against a particular pathogen or to identify antigens correlated with a pathogen inside a sample. Serologic tests are particularly useful for species that are difficult to culture using standard laboratory methods, such as Treponema pallidum (the syphilis-causing agent) or viruses.
Antibodies to a pathogen can be found in a person's blood, indicating that they'd been subjected to that pathogen. Often serologic tests look for immunoglobulin M (IgM) or immunoglobulin G (IgG) antibodies (IgG). IgM is produced in large amounts immediately after an individual is exposed to the pathogen and then rapidly declines.
With the first exposure, IgG is formed as well, but not as rapidly as IgM. Following subsequent exposures, the antibodies formed are mostly IgG, and they stay in the bloodstream for a long span of time. This has an impact on how serology findings are interpreted: a positive IgM result indicates that a person is present or formerly infected, whereas a positive IgG result and a negative IgM result indicates that the individual might be exposed to the virus or immunised in the past. Antibody testing towards infectious diseases is frequently performed in two stages: during the primary illness and then after the patient has recovered.
When the quantity of antibody within every specimen is evaluated, the convalescent specimen has a substantially higher amount of IgG, indicating infection rather than prior exposure. False-negative antibody testing results may be obtained in immunocompromised people, which produce fewer antibodies, and then in individuals who got antimicrobial drugs during the onset of the course of an infection.
2. Transfusion Medicine:
Serologic methods and serology meaning are often used to perform blood typing. Antisera, or reagents containing antibodies, are used to identify the antigens on a person's red blood cells that decide their blood type. Antibodies bind to antigen-expressing red blood cells, causing them to clump tightly (agglutinate), which could be seen visually. Adding plasma to cells that express the corresponding antigen and watching the agglutination reactions may also be used to determine a person's blood group antibodies.
Crossmatching and overt and indirect antiglobulin studies are two other serologic approaches being used in transfusion medicine. Before a blood transfusion, crossmatching is done to make sure that the donor blood is identical. It entails mixing the donor blood cells with the recipient's plasma and watching for agglutination reactions. The direct antiglobulin test is used to determine whether antibodies are bound to red blood cells in the body, which is rare and may arise in situations such as autoimmune hemolytic anaemia, infant hemolytic disease, and transfusion reactions. The indirect antiglobulin test has been used to recognise several blood group antigens and screen for antibodies that might trigger transfusion reactions.
3. Immunology:
By detecting irregular antibodies directed against an individual's own tissues, serologic tests may aid in the diagnosis of autoimmune disorders (autoantibodies). Immunology graphs vary from person to person.
Why a Serological Test?
To understand serologic tests and why they're important, it's helpful to have a basic understanding of the immune system and why people become sick.
Antigens are compounds that cause the immune system (immunology and serology) to respond. They're typically too little for the naked eye to see. They can reach the human body through the mouth, open pores/broken skin, or nasal passages, among other places. The following are examples of antigens that usually affect people:
Fungi
Bacteria
Parasites
Viruses
Antibodies are produced by the immune system to protect from antigens. Antibodies are particles that bind to antigens and render them inactive. Your doctor will detect the type of antibodies and antigens in your blood sample, as well as the kind of infection you have, by testing your blood.
Serology Report
Normal test results: Antibodies are produced by your body in response to antigens. If you don't have any antibodies, that means you don't have an infection. Antibodies are not found in the blood sample, so the results are natural.
Abnormal test results: Antibodies in the blood sample (blood serology) usually indicate that the immune system has responded to an antigen as a result of a current or previous disease or foreign protein exposure.
Antibodies to natural or non-foreign proteins or antigens can be found in the blood, which can help the doctor identify an autoimmune disorder.
The presence of specific antibodies may also indicate immunity to one or more antigens. This means that if you are exposed to the antigen or antigens again, you will not become sick.
Serologic testing can be used to diagnose a variety of diseases, including:
Brucellosis (caused by bacteria)
Measles (caused by a virus)
Amebiasis (caused by a parasite)
Rubella (caused by a virus)
HIV
Fungal infections
Syphilis
Serological Surveys
Serological surveys are frequently used by epidemiologists to evaluate the frequency of a disease within a population, according to a 2016 research paper by Metcalf et al., amongst which were Neil Ferguson and Jeremy Farrar. Random, retrospective sampling among samples was taken for several other medical tests or to determine the susceptibility of antibodies to a particular organism or defensive titre of antibodies inside a population is often used in these surveys.
Serological surveys are commonly used to determine the percentage of people or animals in a population that are positive for a certain antibody, as well as the antibody's titre and concentrations. Such surveys have the ability to be the most straightforward and insightful method for determining the dynamics of a population's susceptibility and immunity. The paper developed a World Serology Bank (also known as a serum bank) and predicted: "related significant methodological advances in serological research, study design, and quantitative analysis, that could cause a step-change in human comprehension and optimal control of infectious diseases."
FAQs on Serological Test
1. What is a serological test?
A serological test is a diagnostic method that examines blood serum to detect the presence of specific antibodies or antigens. The core principle relies on the highly specific binding that occurs in an antigen-antibody reaction. These tests are crucial for identifying infections, autoimmune diseases, and checking for immunity against certain diseases.
2. What does a positive result in a serology test indicate?
A positive serology test result means that the test has detected the specific antibodies or antigens it was designed to find. This typically indicates one of two things:
- Current Infection: The presence of certain antibodies, like IgM, suggests a recent or active infection.
- Past Infection or Immunity: The presence of other antibodies, like IgG, often indicates a past infection or successful vaccination, meaning the person has developed immunity.
3. What are some common examples of serological tests used in medicine?
There are many types of serological tests used for various diagnoses. Some of the most common examples include:
- ELISA (Enzyme-Linked Immunosorbent Assay): Widely used for detecting HIV, pregnancy hormones, and many other conditions.
- Widal Test: A classic serological test used to help diagnose typhoid fever, as mentioned in the Class 12 syllabus on Human Health and Disease.
- VDRL (Venereal Disease Research Laboratory) Test: Used for screening syphilis.
- Complement Fixation Test (CFT): A versatile test for diagnosing infections like brucellosis.
4. What is the fundamental principle behind how serological tests work?
The fundamental principle is immunological specificity. Every antibody is produced to recognise and bind to a unique antigen, much like a key fits only one lock. Serological tests exploit this by using a known antigen to capture a specific antibody from the patient's serum, or vice versa. A subsequent reaction, often producing a colour change (like in ELISA) or clumping (agglutination), makes this binding visible, confirming the presence of the target molecule.
5. What are the main types or categories of serological tests?
Serological tests can be broadly categorised based on the type of reaction they produce:
- Agglutination Tests: In these tests, if the target antibody or antigen is present, it causes visible clumping of particles (e.g., red blood cells in blood typing).
- Precipitation Tests: These involve the reaction of a soluble antigen with a soluble antibody to form a visible, insoluble precipitate.
- Labelled Immunoassays: These are highly sensitive tests where an indicator (like an enzyme, fluorescent dye, or radioisotope) is attached to an antibody or antigen to detect the reaction. ELISA is the most common example in this category.
6. Why might a person test positive on a serological test even if they are no longer sick?
This is a common and important aspect of immunology. A positive result can occur long after recovery because the immune system creates long-lasting 'memory' cells that continue to produce IgG antibodies. These antibodies can persist in the blood for months or even years, providing long-term protection. Therefore, a positive serology test often confirms past exposure and immunity rather than an active, ongoing illness.
7. How is a serological test different from a molecular test like PCR?
The key difference lies in what they detect.
- A serological test looks for the body's immune response to a pathogen by detecting antibodies or antigens (proteins).
- A molecular test like PCR (Polymerase Chain Reaction) looks for the pathogen's own genetic material (DNA or RNA).
8. Is blood typing considered a serological test?
Yes, blood typing is a classic example of a serological test. Specifically, it is an agglutination test. The procedure involves mixing a person's red blood cells with known antibodies (anti-A and anti-B serum). If the corresponding antigens are present on the red blood cells, the antibodies will cause them to clump together (agglutinate), allowing for the determination of the blood type (A, B, AB, or O).
9. In what situations are serological tests more useful than trying to culture the pathogen in a lab?
Serological tests are often preferred when the causative agent is difficult, slow, or dangerous to grow (culture) in a laboratory. For example, some viruses and bacteria, like the syphilis spirochete or certain microorganisms without cell walls like PPLO (Mycoplasma), do not grow well on standard media. In these cases, detecting the body's antibody response through serology is a much more practical and effective diagnostic strategy.
