ELISA: Treatment, Effect & Risks

The ELISA test is a laboratory medical examination, during the performance of which a so-called antigen-antibody reaction occurs. Different antigens can be tested that play a role in human or veterinary medicine. Only accredited laboratory institutes are commissioned to perform the test in Germany.

What is procedure?

Within laboratory medical examinations, the ELISA test belongs to the so-called immunological procedures. Through the test procedure, protein molecules can be detected in quite different body fluids. ELISA is the abbreviation for Enzyme Linked Immuno Sorbent Assay. It is therefore an English-language designation that has, however, become established in German medical usage. The ELISA test belongs to the so-called immunological procedures within laboratory medical examinations. The test procedure can be used to detect protein molecules in a wide variety of body fluids. The detection of these molecules in turn allows conclusions to be drawn about certain diseases or clinical pictures, which is why doctors also make their diagnosis dependent on the result of such an ELISA test. The test procedure is therefore of great importance in everyday clinical practice, whether in an outpatient or inpatient setting. The corresponding body fluids, for example whole blood or fluids from joints, are sent to the laboratory immediately after being collected from the patient. These are usually quite urgent samples, because the native material is considered sensitive and should be examined as quickly as possible. So-called overstored samples can lead to false negative results because the pathological proteins to be detected have been reduced or completely degraded in the meantime. Thus, so-called preanalytics play an important role in ELISA; suspicious or negative results should be repeated again if appropriate clinical symptoms are present.

Function, effect, and goals

For correct test performance in an accredited medical laboratory, test tubes and so-called microtiter plates are absolutely necessary. These plates with fine semi-concave indentations are made of special plastic and are each coated with a very specific antibody. If the antigen to be detected is present in a body fluid to be examined, then a specific antigen-antibody reaction occurs according to the so-called lock-and-key principle. The sample material can be inserted into the plates either manually by laboratory personnel using pipettes or fully automatically. In modern laboratory medical institutes, only fully automated systems are used for ELISA diagnostics. However, these must be monitored by trained personnel, medical-technical laboratory assistants. The so-called internal and external quality control is also the responsibility of the laboratory staff, superior to the medical staff for laboratory medicine, infectious disease epidemiology and microbiology. After the first test batch, i.e. after the material has been pipetted onto the plates, the specific antigens in the sample, if present, have already bound to the antibodies on the plastic plate. A wash with physiological saline is then performed to remove interfering factors such as unwanted antigens or proteins from the preparation. This step is very important to avoid false positive reactions. A false positive result interpreted by the laboratory can have fatal consequences for a patient. In the second step of the test, another antibody is added that is coupled to an enzyme. This labeled antibody also binds to the antigen. In a third and final step, a special dye is added in a defined amount, which is degraded to a greater or lesser extent by enzyme residues that are still present. Only such enzyme can be degraded, which was not previously bound to the antigen together with the antibody. The free enzyme is able to cleave the added dye. The exact amount of the cleaved dye can be precisely determined with another laboratory method, the so-called photometry. This enables precise conclusions to be drawn as to whether antigen is present in a sample material at all and, if so, how much.The ELISA test is used not only for the initial diagnosis or to confirm suspected diagnoses of certain diseases and clinical pictures, but also to monitor their progress. If the antigen concentration in the test becomes lower during the course of therapy, the therapy is considered successful.

Risks, side effects, and hazards

The ELISA test obtains its informative value primarily through the detection of antigenic structures in body fluids. The test allows a so-called qualitative, but also semi-quantitative and quantitative statement about the suspected presence of certain antigens in body fluids. Whole blood cannot be used for the test, only blood serum. A direct test on the patient, for example from the capillary blood of the fingertip, is therefore, as with some other serological tests, not possible to date. In human medicine, the ELISA test is primarily used to detect antigens in bacterial, viral or fungal infections. In addition, all positive results of hepatitis serology are checked again with an ELISA test as standard. Certain hormones, for example the pregnancy hormone HCG, can also be determined with the ELISA test. If certain complications occur during pregnancy, precise knowledge of the concentration of the pregnancy hormone in the blood is very helpful diagnostically and therapeutically. Another indication for the test is the detection of so-called paraproteins in the urine, as they occur, for example, in various tumor diseases, such as multiple myeloma. The ELISA test is still performed in many laboratories today, but is considered outdated by experts. The immune reaction coupled to enzymes in the ELISA test has been increasingly replaced in recent years by radioactively labeled antibodies, which provide an even better quantitative measurement result. These tests are also called RIA, Radio Immunabsorbent Assay. Other specific advancements of ELISA are light chemical methods such as luminescence or fluorescence.