A The Coombs test (also known as antiglobulin test or AGT ) is one of two clinical blood tests used in immunohematology and immunology. Two Coombs tests are direct Coombs test ( DCT , also known as direct antiglobulin test or DAT ), and < b> indirect Coombs test (also known as indirect antiglobulin test or IAT )
The Coombs test is directly used to test for autoimmune hemolytic anemia; that is, the condition of low red blood cell count (a.k.a.RBCs) caused by immune system lysis or rupture of the RBC membrane leading to RBC destruction.
In certain diseases or conditions, a person's blood may contain IgG antibodies that can specifically bind to the antigen on the RBC surface membrane, and circulating red blood cells can be coated with IgG alloantibodies and/or IgG autoantibodies. The complementary protein may then bind to the bound antibody and cause RBC destruction.
The direct Coombs test is used to detect antibodies or complementary proteins bound to the surface of red blood cells; blood samples were taken and red blood cells were washed (remove the patient's own plasma) and then incubated with anti-human globulin (also known as "Coombs reagent"). If this produces red cell agglutination, the Coombs test is directly positive, a visual indication that antibodies (and/or complementary proteins) are bound to the surface of red blood cells.
The indirect Coombs test is used in prenatal testing of pregnant women and in blood testing prior to blood transfusion. It detects antibodies against red blood cells that are present unattached in the patient serum. In this case, the serum is taken from the blood sample taken from the patient. Then, serum is incubated with red blood cells from known antigenicity; that is, red blood cells with known reference values ​​from other patients' blood samples. Finally, anti-human globulin is added. If agglutination occurs, the Coombs test is not directly positive.
Video Coombs test
Mekanisme
Two Coombs tests are based on the fact that anti-human antibodies, produced by immunization of non-human species with human serum, will bind human antibodies, usually IgG or IgM. Animal anti-human antibodies will also bind human antibodies that can be repaired to the antigen on the surface of red blood cells (also referred to as RBCs), and under appropriate test tube conditions this may cause red blood cell agglutination. The phenomenon of red blood cell agglutination is important here, since the results of red blood cell clotting can be visualized; when the aggregation looks positive test and when the lump does not look the test is negative.
Common clinical uses of the Coombs test include blood preparation for transfusion on cross-matching, atypical antibodies in the blood plasma of pregnant women as part of antenatal care, and antibody detection for the diagnosis of immune-mediated hemolytic anemia.
The Coombs test was performed using RBCs or serum (directly or indirectly, respectively) from intact vein blood samples taken from patients with venipuncture. Venous blood is brought to a laboratory (or blood bank), where scientific trained technical staff performs the Coombs test. The clinical significance of these results was assessed by physicians who requested the Coombs test, perhaps with the help of a laboratory-based hematologist.
Maps Coombs test
Direct Coombs test
Direct Coombs tests (also known as direct antiglobulin tests or DAT) are used to detect whether antibodies or complementary system factors are attached to the RBC in vivo surface antigen . DAT is currently not required for pre-transfusion testing but may be included by some laboratories.
Examples of diseases that give positive direct Coombs tests
The Coombs test is directly used clinically when immune mediated hemolytic anemia (antibody-mediated RBCs destruction) is suspected. The positive Coombs test shows that the immune mechanism attacks the patient's own red blood cells. This mechanism may be an autoimmunity, alloimmunity or drug-mediated drug-induced mechanism.
Examples of alloimmun hemolysis
- Hemolytic disease in newborns (also known as HDN or fetal erythroblastosis)
- Rh D hemolytic disease in newborns (also known as Rh disease)
- ABO hemolytic disease in newborns (direct Coombs test may be only weak positive)
- Anti-Kell hemolytic disease in newborns
- Rh hemolytic disease in newborn
- Rh E hemolytic disease in newborn
- Other blood group misfits (RhC, Rhe, Kidd, Duffy, MN, P and others)
- Alloimun hemolytic transfusion reaction
Examples of autoimmune hemolysis/immunohemolytic hemolysis
- Autoimmune antibody hemolytic anemia
- Idiopathic
- Systemic lupus erythematosus
- Evans syndrome (antiplatelet antibody and hemolytic antibody)
- Anemia of immunohemolytic cold antibodies
- idiopathic cold haemagglutinin syndrome
- Waldenström macroglobulinemia
- Infectious mononucleosis
- Paroxysmal cold hemoglobinuria (rare)
Drug-induced immune hemolysis
- Methyldopa (type 2 mediated IgG hypersensitivity)
- Penicillin (high dose)
- Quinidine (IgM activation mediated classical complement line and Complex membrane attack, MAC)
(The memory device to remember that DAT tests red blood cells and is used to test the baby for hemolytic hemolytic disease in newborns is: R h D isease R = RBC, D = DAT.)
Laboratory methods
The patient's red blood cell is washed (removing the patient's own serum) and then centrifuged with antihuman globulin (also known as Coombs reagent). If immunoglobulins or complementary factors have been improved on the in-vivo RBC surface, antihuman globulin will agglomerate red blood cells and direct Coombs tests will be positive. (Visual representation of the positive direct Coombs test is shown at the top of the scheme).
Indirect Coombs test
Indirect Coombs tests (also known as indirect antiglobulin tests or IAT) are used to detect intra-vitro antibody reactions. This is used to detect very low antibody concentrations present in plasma/serum patients prior to blood transfusion. In antenatal care, IAT is used for screening pregnant women for antibodies that can cause hemolytic disease in newborns. IAT can also be used for compatibility testing, antibody identification, RBC phenotype, and titration studies.
Example of clinical use of indirect Coombs test
Preparation for blood transfusion
The Coombs test is not directly used for antibody screening in blood preparation for blood transfusion. Blood donors and recipients should be ABO and Rh D compatible. Blood donors for transfusions are also screened for infection in a separate process.
- An antibody check
Blood samples from recipients and blood samples from each donor blood unit were screened for antibodies with indirect Coombs tests. Each sample was incubated against various red blood cells that together showed various surface antigens (ie blood type).
- Cross matching
The indirect Coombs test was used to test samples of serum recipients for antibodies against red blood cell blood donor samples. This is sometimes called cross matching blood.
Antenatal antibody check
The Coombs test is not directly used for screening pregnant women for IgG antibodies that tend to cross the placenta into fetal blood and cause hemolytic disease in newborns.
Laboratory methods
The IAT is a two-stage test. (Cross matches are displayed visually at the bottom of the scheme as an indirect Coombs test sample).
First stage
The test washed red blood cells (RBCs) incubated with known human serum. If the serum contains antibodies to the antigen on the RBC surface, the antibodies will bind to the surface of red blood cells.
Second stage
The red blood cells are washed three or four times with an isotonic salt solution and then incubated with antihuman globulin. If antibodies are attached to RBC surface antigen in the first stage, red blood cells will agglutinate when incubated with antihuman globulin (also known as Coombs reagent) at this stage, and indirect Coombs tests will be positive.
Titration
By diluting serum containing antibodies, the quantity of antibodies in the serum can be measured. This is done by using a doubled dilution of the serum and finding the maximum dilution of the serum test that is capable of producing the relevant red blood cell agglutination.
Coombs reagent
The Coombs reagent (also known as Coombs antiglobulin or antihuman globulin ) is used in either the direct Coombs test or the indirect Coombs test. The Coombs reagent is an antihuman globulin. This is made by injecting human globulin into animals, which produces polyclonal antibodies specific to human immunoglobulin and human complement system factors. More specific Coombs reagents or monoclonal antibodies may be used.
Additional media
Both IgM and IgG antibodies bind strongly with their antigens. The most reactive IgG antibodies are at 37 ° C. IgM antibodies are easily detected in saline at room temperature because IgM antibodies are able to bridge between RBCs because of their large size, efficiently creating what is seen as agglutination. IgG antibodies are smaller and require help to bridge well enough to form visual agglutination reactions. The reagents used to enhance IgG detection are referred to as potentiators. The red blood cells have a net negative charge called zeta potential that causes them to have a natural repulsion of each other. Potentiators reduce the zeta potential of RBC membranes. Common potentiators include low ion-ionic solutions (LISS), albumin, polyethylene glycol (PEG), and proteolytic enzymes.
History
The Coombs test was first described in 1945 by Cambridge immunologist Robin Coombs (after whom his name), Arthur Mourant and Rob Race. Historically, it was done in a test tube. Today, it is generally done using microarray and gel technology.
References
External links
- Test Coombs Online - Test Coombs Online
- Testing Coombs - Institute of Transfusion Medicine.
- The Coombs test - live - Medlineplus.org.
- The Coombs test - indirect - Medlineplus.org.
- Acute anemia - emedicine.com
- Drugs that cause hemolytic anemia - Merck Manual.
- The Coombs Test at the National Library of Medicine US Subject Medical Subject (MeSH)
Source of the article : Wikipedia
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