Antibody screening test
The antibody search test, or indirect Coombs test, is a blood serum test that detects antibodies against certain characteristics of red blood cells ( erythrocytes ) and against certain infectious diseases . In addition to the indirect Coombs test, there is also the direct Coombs test . In this respect, the term 'Coomb test' is not to be equated with the 'antibody search test'.
execution
The patient's blood serum (which contains the antibodies to be searched for) is combined with the antigens to be tested (so-called test erythrocytes from donor blood, for which the antigens present are known).
If antibodies of the IgM class against the antigens are present in the serum, the mixture already clumps in this step of the test and the test result is therefore positive.
If the test is negative up to this point, incomplete antibodies (i.e. non-clumping) of the IgG class can be detected indirectly. In this step, Coombs serum (anti-human globulin) is also added, i.e. rabbit antibodies against human antibodies. Here, too, clumping means a positive test result.
If an antibody screening test carried out simultaneously with several antigens has a positive result, further tests must be carried out to determine which of the antigens caused the reaction (differentiation). With regard to the ability of the antibodies to cause hemagglutination or clumping of red blood cells, a distinction is made :
- Direct (active) hemagglutination: Specific antibodies bind to certain molecules on the cell surface of the erythrocytes , for example through IgM antibodies.
- Indirect (inactive) hemagglutination: First, antigens are bound to the surface of the erythrocytes. Antigen-homologous antibodies then bind to these, for example through the Coombs serum (anti-human globulin) and the IgG antibodies.
Antibody screening test for pregnancy and blood transfusions
Every person or mother has natural or regular antibodies ( isoagglutinins ) against antigens of foreign red blood cells during pregnancy . Blood group AB of the AB0 system is an exception. The term isoagglutinin or the regular antibody describes a specific reaction form of a serum antibody that is directed against antigenic characteristics of the AB0 blood group system . Isoagglutinins arise in the first months of life when the child comes into contact with antigens of bacterial origin ( cross-immunity ), which epitopes resemble the AB0 antigens . Since no antibodies are normally formed against the body's own characteristics, the antibodies that correspond to one's own blood group are missing . The serum from humans e.g. B. with blood group A contains isoagglutinin anti-B, i.e. the antibody against blood group substance B and thus also against blood group B. If a person with blood group A comes into contact with blood group B through a faulty blood transfusion , for example it a hemagglutination ( immune complex ) and the corresponding clinical consequences for the people of blood type A. isoagglutinines are mostly from the IgM isotype, but also from the IgG type.
The antibody search test also finds irregular antibodies that can arise, for example, two to three days after the mother's and child's blood has mixed during childbirth or after a blood transfusion . They can then lead to incidents during subsequent blood transfusions or pregnancies. This is because irregular antibodies are antibodies which (in contrast to isoagglutinins or blood group antigens ) were formed by unnatural sensitization (e.g. through blood transfusions, pregnancy). For example with the rhesus factor , because the antibodies of the rhesus system are almost exclusively so-called immune antibodies. Their formation is stimulated by the transfer of genetically different blood from other people. Naturally occurring rhesus-like antigens have not yet been detected. The formation of so-called natural antibodies through cross immunity as in the case of the AB0 system is unlikely.
For the antibody screening test, the patient's serum is combined with red blood cells that contain the antigens to be tested. Rhesus incompatibility is excluded by default , but antigens such as those of the Kell , Duffy and MNS systems are also tested. In the vast majority of cases, the antibody test remains negative; if the result is positive, the rhesus antibodies are among the most common antibodies found after differentiation.
Remarks
- ↑ Both spellings are common: "antibody search test" or "antibody search test"
- ↑ Further designation: indirect antihuman globulin test, in short: indirect AHG test
See also
Individual evidence
- ↑ Immune antibodies are the irregular isoantibodies directed against blood group antigens or leukocyte antigens (epitopes), which only appear after prior sensitization
- ↑ Relevance of a positive antibody screening test (AKS) in pregnancy. (No longer available online.) In: Lab 28. Labor 28, archived from the original on March 7, 2015 ; Retrieved on January 3, 2010 (December 2006 edition): "About 99% of pregnant women have no relevant antibodies against erythrocytes detectable." / "Frequency with positive AKS: Anti-D 13%, Anti-E 11%, Anti-M 11%, Anti-c 6%, Anti-Le a 6%, Anti-C 6%, Anti-Jk a 4% , Anti-S 4%, Anti-Le b 4%, Anti-C w 4%, Anti-P 1 4%, Anti-K 3% "" Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.
