A family practice physician in rural Maine obtains a blood sample, isolates the RBCs, removes the antibodies and adds antihuman globulin. He note that the erythrocytes aggregate. How would you interpret these results?
A. Negative direct Coombs test
B. Positive indirect Coombs test
C. Colonic adenocarcinoma
D. Negative indirect Coombs test
E. Positive direct Coombs test
The patient in question has a hemoglobin value of 7.4 g/dL and an elevated serum unconjugated bilirubin. Which is the likely diagnosis?
A. Paroxysmal nocturnal hemoglobinuria
B. Traumatic hemolysis
C. Hereditary elliptocytosis
D. Systemic lupus erythematosus
E. Erythroblastosis fetalis
Both direct and indirect tests are antigen-antibody reactions. Differences:
Direct Coombs Test
Indirect Coombs also tests for a reaction, but
- Uses patient’s RBCs, which are washed clear of plasma, and then incubated with a known antibody.
- If they agglutinate, then the direct test is positive.
- Test for autoimmune hemolytic anemia
- Uses patient’s serum (not rbcs).
- Patient’s serum is added to rbcs that are known to have a certain antigenicity.
- If the serum contains the suspected antibodies, then there will be a reaction, and the test is positive.
- Screen pregnant women for the presence of antibodies that could cause hemolytic disease of the newborn.
- It is also used in cross matching blood before transfusion.
direct—-rbc already have attached antibody..only add anti human ig
indirect-to test for antibody—add rbc to the serum,n then add anti human ig
Coombs test (aka Coombs’ test, antiglobulin test or AGT) refers to two clinical blood tests used in immunohematology and immunology.
Direct Coombs test (aka s direct antiglobulin test or DAT)
Indirect Coombs test (aka indirect antiglobulin test or IAT)
The direct Coombs test is used to detect red blood cells sensitized with igG alloantibody, IgG autoantibody, and complement proteins. It detects antibodies bound to the surface of red blood cells in vivo. The red blood cells (RBCs) are washed (removing the patient’s own plasma) and then incubated with antihuman globulin (also known as “Coombs reagent”). If this produces agglutination of the RBCs, the direct Coombs test is positive.
The indirect Coombs test is used in prenatal testing of pregnant women, and in testing blood prior to a blood transfusion. It detects antibodies against RBCs that are present unbound in the patient’s serum. In this case, serum is extracted from the blood, and the serum is incubated with RBCs of known antigenicity. If agglutination occurs, the indirect Coombs test is positive