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In 1945 the antiglobulin test was introduced by R.R. Coombs. The test was used to test and detect the non-agglutinating antibodies of the red blood cells or the sensitized red cells. Direct antiglobulin test DAT is used to test C3 or 1gG which is bound or attached to the exterior or surface of the cells Segel and Marshall 155 . DAT is useful in finding outwhether there is immune etiology amongst the patients with hemolysis. The non-immune causes of hemolysis which includes red cell enzyme deficiencies, purpura, mechanical hemolysis, burns, and heredity spherocytosis will majorly have a negative DAT while the immune cause of hemolysis such as drug-induced hemolysis, anemias, or hemolytic transfusions shows a positive DAT. A positive DAT may occur without hemolysis. A positive DAT which is caused by C3 complement alone is majorly seen in patients with paroxysmal cold hemoglobinuria and induced hemolytic anemias Segel and Marshall 160 . The present offending antibodies are of 1gM isotypes which efficiently binds with the complement Karp . 1gm antibodies are usually not detected by the DAT directly, but rather due to the presence of C3 on the red blood surfaces autoantibodies. Testing DAT in the blood takes between five to ten minutes. It is carried out by incubating or reacting the patient s red blood cells with the Coombs reagent. In most patients who have warm autoantibodies, an affirmative or positive DAT is majorly due to 1gG.
Nearly a third of these patients also may be having C3 in their red cell membranes Karp . Red cells also coated with 1gG have also been seen in patients who received an incompatible transfusion. Thus, to ascertain whether a transfusion is mandatory or not, DAT is usually performed. On the process, the 1gG which is bound to the surface of the red cells is determined and eluted. Eluted autoantibodies majorly bind to all the red cells but also have specificity with the Rh system while the eluted alloantibodies maybe gave specificity. The red cells which are sensitized with 1gG may be destroyed by hemolysis performed intravascularly. Indirect antiglobulin test IAT is majorly used to test red blood cells antibodies in patient s serum also stated or referred to as antibody screening Yeow, Heather, and Gil . Nearly 5% of all patients have a positive IAT as a result of IgM antibodies, IgG antibodies or both of them. IAT test is carried out by incubating the client s or patient s serum with the reagent for 1800 seconds. The agglutination of the red cells is then observed. If the antibody screening is positive, further testing is done to note the specific type of the antibody present.
During the screening process, if transfusion is necessary, the patients with the significant red cells alloantibodies identified during the antibody screening process should each receive antigen which is of negative red cells. Comparing the two processes, IAT is used to find out the existence of antibodies in the blood plasma while the DAT is used to find out whether red blood cells are coated with immunoglobin, complement, or both Karp.
Additionally, IAT is also used to note or identify the clinically important red blood cell alloantibodies which are vital in selecting of choosing compatible or well-matched blood samples or products for transfusion while on the other hand; DAT is used find or determine whether patients with hemolysis have immune etiology. The two processes are also characterized by some similarities. Both DAT and IAT are interrelated processes used in determining blood transfusion compatibility. They are used in the blood bank to detect the type of antibodies in both the serum and the red cells. The information is later used to find the appropriate transfusion type. The test is also carried out by incubation of the plasma and the red cells. The incubation process allows for agglutination which is applicable for both tests. DAT IAT Testing antibody in serum Testing red blood cells coating. To identify red cell alloantibodies To identify patients with hemolysis who have immune etiology.
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