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What is Coombs Test?

Coombs test (also known as Coombs' test, antiglobulin test or AGT) refers to two clinical blood tests used in immunohematology and immunology. The two Coombs tests are the direct Coombs test (also known as direct antiglobulin test or DAT), and the indirect Coombs test (also known as indirect antiglobulin test or IAT).


Purpose of Test

The Direct Coombs' test is used to detect antibodies that are already bound to the surface of red blood cells. Many diseases and drugs (quinidine, methyldopa, and procainamide) can lead to production of these antibodies.These antibodies sometimes destroy red blood cells and cause anemia. This test is sometimes performed to diagnose the cause of anemia or jaundice.
The indirect Coombs' test looks for unbound circulating antibodies against a series of standardized red blood cells.The indirect Coombs' test is only rarely used to diagnose a medical condition. More often, it is used to determine whether a person might have a reaction to a blood transfusion.


Test of Result Interpretation

No clumping of cells (agglutination), indicating that there are no antibodies to red blood cells, is normal. An abnormal (positive) direct Coombs' test means you have antibodies that act against your red blood cells. This may be due to:

  • Autoimmune hemolytic anemia without another cause
  • Chronic lymphocytic leukemia or other lymphoproliferative disorder
  • Drug-induced hemolytic anemia (many drugs have been associated with this complication)
  • Erythroblastosis fetalis (hemolytic disease of the newborn)
  • Infectious mononucleosis
  • Mycoplasmal infection
  • Syphilis
  • Systemic lupus erythematosus or another rheumatologic condition
  • Transfusion reaction, such as one due to improperly matched units of blood

The test is also abnormal in some people without any clear cause, especially among the elderly. Up to 3% of people who are in the hospital without a known blood disorder will have an abnormal direct Coombs' test. An abnormal (positive) indirect Coombs' test means you have antibodies that will act against red blood cells your body views as foreign. This may suggest:

  • Autoimmune or drug-induced hemolytic anemia
  • Erythroblastosis fetalis hemolytic disease
  • Incompatible blood match (when used in blood banks)

Preparation

No preparation required.


Turnaround Time

Daily