- Serological tests - indications for the test
- Serological tests - what are they?
- Serological tests - results
Help the development of the site, sharing the article with friends!
Serological tests are one of the basic laboratory tests commonly used in the diagnosis and monitoring of various diseases. Serological tests allow the detection of antigens and / or antibodies in biological material. What are the types of serological tests? What are the indications for performing these tests?
Serological testsare immunological tests, the purpose of which is to detect antigens or antibodies in the tested biological material. Antigens are molecules that the immune system recognizes as foreign. Antigens can be bacteria, viruses, fungi, protozoa, pollen, food, and in some cases even your own tissues.
In contrast, antibodies are immune proteins that are produced against antigens. Each antibody is produced specifically against a specific antigen, and the body, depending on the situation, can produce antibodies in various classes: IgA, IgM, IgG, IgE, IgD.
Serological tests - indications for the test
The indication for serological tests is the suspicion of diseases such as:
- Infectious diseases
Serological examination is widely used in the diagnosis of viral, bacterial and fungal diseases. In the course of an immune response against microbes, specific antibodies are produced by B lymphocytes. In laboratory diagnostics, IgM antibodies and IgG antibodies are mainly used.
The determination of specific IgMs allows the detection of active microbial infections, as they are produced first in the immune response. Over time, IgM antibodies are replaced by more persistent IgG antibodies, the determination of which indicates a persistent infection or simply contact of the organism with the microorganism in question. An example is the assessment of the level of antibodies in the IgM and IgG classes in the diagnosis of Lyme disease.
Serological methods can also directly detect the presence of microbial antigens in the blood or faeces. In this way, for example, the presence of Helicobacter pylori in the gastrointestinal tract is diagnosed. The method is based on the determination of the bacterial antigen in the stool. This test is highly sensitive and specific.
- Parasitic diseases
Serological methods can be helpful in diagnosing parasitic infestations, but they cannot confirm the diagnosis on their own. As with infectious diseases, serological methods are used to assess the presence of parasite antigens or antibodies raised against them. Serological methods for detecting antibodies are important in diagnostics, among others. trichinosis, echinococcosis, toxocarosis. In the stool, however, antigens of parasites such as lamellae can be determined.
GOOD TO KNOW: Blood tests for parasites - what are they?
- Diseases with autoimmunity
In some situations, the immune system begins to recognize its own tissues as antigens (so-called autoantigens) and make antibodies against them, resulting in the emergence of autoimmune disease. Therefore, the presence of anti-tissue antibodies can be detected by serological tests.
An example is the assessment of the blood level of anti-thyroid antibodies: anti-thyroid peroxidase (anti-TPO), anti-thyroglobulin (anti-Tg) and anti-TSH (anti-TSHR) antibodies, the determination of which is helpful in the diagnosis of autoimmune diseases of the thyroid gland (Graves' disease, Hashimoto's disease).
Serology is the study of antigen reactions with blood serum antibodies.
- Allergic diseases
The body can also make antibodies to pollen, food and dust mites, which are called allergens. The most common are IgE antibodies that cause allergic diseases. Both total IgE and allergen-specific IgE are measured by serological methods.
CHECK: ALLERGY UNDER THE MAGNIFYING: what is the mechanism of allergy?
- Determining blood groups in transfusion medicine
Red blood cells have characteristic antigens in their air, and their differentiation in the human population is the basis for distinguishing blood groups.
Serological methods are an important element in determining blood groups in transfusion medicine in the so-called the main group system (A, B, AB, 0), Rh factor (+, -) and Kell (the main antigen is marked with the letter K).
An example of the use of serological tests in transfusion medicine is the diagnosis of haemolytic post-transfusion reactions. Performing serological tests in this case is aimed at determining the cause of the reaction and indicating preparations that the patient may receive.
- Diagnosis of serological conflict in pregnancy
In case the child's parents differ in their antigensin any blood group system, you may develop what is known as serological conflict. The most common serological conflict occurs in the Rh system and in 85% of cases it concerns the D antigen of this system. In serological conflict, antibodies against the baby's red blood cells are produced and destroyed as IgG antibodies pass through the placenta.
The reason for this is the earlier contact of the mother with the blood of the fetus, which is incompatible with antigen, which takes place, for example, during the delivery of the first child and the production of IgG antibodies against the D antigen in the Rh system (alloantibodies). In the next pregnancy, these antibodies penetrate the fetus, causing the breakdown of its red blood cells.
A serological conflict occurs when the RhD mother is negative (RhD-) and the baby is positive (RhD +). Testing for alloantibodies by means of serological tests should be performed in all pregnant women up to the 10th week of pregnancy, between 21-26 weeks of pregnancy only in RhD- women who were not detected in the first test, and between 27-32 weeks of pregnancy in each woman.
Worth knowingSerological tests - types
- agglutination reaction
- neutralization reaction
- complement fixation reaction
- precipitation reaction
- antiglobulin test (Coombs test)
- hemagglutination inhibition test
- immunohistochemical methods
- immunonephelometric method
- immunoturbidimetric method
- immunoenzymatic methods (ELISA test)
- immunofluorescence (IF) methods
- radioimmunoassay methods (RIA)
- Western blot method
Serological tests - what are they?
Serological tests use the properties of the antigen and the antibody to create the so-called immune complexes. By modifying monoclonal antibodies, e.g. by attaching fluorescent dyes or enzymes to them, specific molecules in biological material can be detected.
For serological testing, blood is usually taken from the elbow flexion, but serological testing is also performed from saliva, urine, faeces, cerebrospinal fluid, and tissue specimens.
Serological tests - results
The interpretation of the serological test varies depending on the indication for which it was performed. We should also remember that testing antibodies against microorganisms is a test of their indirect presence in the organism and in some cases it may only indicate contact with a given pathogen in the past.
The same is with presenceantibodies to your own tissues. Some of them also occur in he althy people, therefore the results of serological tests should be interpreted together with other laboratory tests and clinical symptoms of the patient.
Worth knowingWhat is a serological window?
This term is used in the diagnosis of infectious diseases and means the period from the moment of infection with a pathogen until the body produces specific antibodies against the pathogen. Usually, this period lasts from several to several weeks. During the serological window, the results of serological tests may give a false negative result and other diagnostic methods, e.g. genetic tests, should be used for diagnosis.
References
- Laboratory diagnostics with elements of clinical biochemistry, a textbook for medical students edited by Dembińska-Kieć A. and Naskalski J.W., Elsevier Urban & Partner Wydawnictwo Wrocław 2009, 3rd edition
- Internal diseases, edited by Szczeklik A., Medycyna Praktyczna Kraków 2010
- Alhabbab R.Y. Basic Serological Testing. Springer International Publishing AG 2022
Karolina Karabin, MD, PhD, molecular biologist, laboratory diagnostician, Cambridge Diagnostics Polska A biologist by profession, specializing in microbiology, and a laboratory diagnostician with over 10 years of experience in laboratory work. A graduate of the College of Molecular Medicine and a member of the Polish Society of Human Genetics. Head of research grants at the Laboratory of Molecular Diagnostics at the Department of Hematology, Oncology and Internal Diseases of the Medical University of Warsaw. She defended the title of doctor of medical sciences in the field of medical biology at the 1st Faculty of Medicine of the Medical University of Warsaw. Author of many scientific and popular science works in the field of laboratory diagnostics, molecular biology and nutrition. On a daily basis, as a specialist in the field of laboratory diagnostics, he runs the content department at Cambridge Diagnostics Polska and cooperates with a team of nutritionists at the CD Dietary Clinic. He shares his practical knowledge on diagnostics and diet therapy of diseases with specialists at conferences, training sessions, and in magazines and websites. She is particularly interested in the influence of modern lifestyle on molecular processes in the body.