Immunological tests can be used in a variety of studies and for very different purposes – whether in an allergy suspected, for the early detection of colorectal cancer or pregnancy test. The tests are used for routine laboratory examinations in clinics and laboratory practices, as quick tests at home and in private practices.
How does the proof work?
Immunological methods can be used to detect specific substances or pathogens in the body – for example, viruses, hormones or the blood pigment hemoglobin. To do this, they use the defence mechanism of the body: To ward off pathogens or foreign substances, the immune system forms so-called antibodies. These are proteins that are constructed like keys to a lock exactly matching the pathogen or foreign body. Antibodies trap them, neutralize them and attract more defence cells.
For an immunological test in the laboratory, antibodies are produced biotechnologically, which match exactly the substance or pathogen sought. When these antibodies are combined with a blood, urine or stool sample, and the sample contains the appropriate counterpart, both bind together. This reaction is the detection of the suspected pathogen or the substance in question.
How is the examination performed?
Immunological tests, therefore, contain particular antibodies that combine with the substance of interest in the sample. In some experiments, the compound is visible to the naked eye: for example, the blood clumps on a blood-typed test card. In other operations, the connection with a luminous material or an enzyme must first be made visible.
A distinction is made between rapid tests and a precise analysis in the laboratory:
In a laboratory analysis, the amount of bound antibody is measured by sensitive equipment based on the intensity of a light or colour reaction. It corresponds to the amount of substance sought. A laboratory examination takes longer but is more accurate than a quick test.
In a rapid immunological test, the antibodies are applied to a carrier. Mostly it is a piece of paper, and sometimes the shuttle is also made of glass. Quick tests are easy to handle, and the result is immediately available. However, these tests are not as sensitive as laboratory tests, and they can not prove the exact amount of substance sought.
A quick test works according to the principle of the so-called “lateral flow test” or the lateral flow test:
If the test strip is moistened on one side with the liquid sample (for example urine), the substance sought binds to antibodies that are located on the piece. After that, the liquid slowly migrates through the porous paper to the other side. This results in further compounds of the substance sought and antibodies that cause a colour. When enough liquid has been applied, it continues to flow to the other end of the paper strip. There is a control strip. If this also turns on, the test was carried out correctly.
What are immunological tests used for?
Immunological test methods are widely used. Some application examples are:
Colorectal cancer screening: The so-called stool test looks for the blood pigment hemoglobin as a sign of blood in the stool. Blood in the stool may indicate hemorrhoids, as well as polyps or colon cancer.
Allergy tests: for the detection of antibodies to allergenic substances such as grass pollen or certain foods.
Pathogen detection in infections: If suspected bacterial tonsillitis or scarlet fever the test looks for streptococci. If a Borrelia infection (borreliosis) is suspected after a tick bite, he or she can detect the bacteria themselves or antibodies to Borrelia. Viruses can also be detected by immunoassays, such as Hepatitis C, HI or HP viruses. During pregnancy, a blood test can tell if a woman is immune to toxoplasmosis.
Diagnosis of myocardial infarction and thrombosis: Shortly after a heart attack or thrombosis, there are elevated levels of specific proteins in the blood. An immunoassay can detect them.
Urine examination: If the rapid test finds sugar, blood, protein or inflammatory cells in the urine, this may indicate diabetes, urinary tract infections or kidney damage.
Pregnancy test: With the quick check, a woman can determine if her urine contains the pregnancy hormone Beta-HCG.
Drug and drug rapid tests: Immunological tests are also used to detect drugs such as cannabis, ecstasy, cocaine. Even medications with an effect on the central nervous system, such as sleeping pills (benzodiazepines), amphetamines or morphine can be detected.
Blood grouping: Before blood transfusions, the blood group identity between donor and recipient is determined by immunological test methods.
Other areas of application include the diagnosis of congenital and acquired diseases of the immune system, the differentiation of different forms of rheumatism and the control of the course of an existing condition, such as certain tumour diseases (PSA value in the blood in prostate cancer).
The antibody principle also makes use of tests in doping control, food hygiene or pollutant testing.