Q22 - Direct and Indirect Coombs Tests

Theoretical 2 Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

There are two clinical tests to detect some antibodies against erythrocytes (RBCs), direct coombs test and indirect coombs test. During the direct coombs test a blood sample is taken from a person. RBCs are washed (removing the patient’s own plasma) and then incubated with anti-human globulin, which attaches to all IgG antibodies. Coombs test is positive if agglutination reaction occurs. In the indirect coombs test, serum is extracted from the blood sample taken from the person. Then, the serum gets incubated with RBCs of known antigenicity and is washed. Finally, anti-human globulin is added. If agglutination occurs, the indirect coombs test is positive.

Using the information and data, determine which of the statements are true or which are false.

A. Direct coombs test will be positive only if autoantibodies are present.

B. If the result of indirect coombs test using serum of patient 1 and RBCs of patient 2 is positive, so we can use the patient 2 as a blood donor for patient 1.

C. Anti-human globulin specifically binds to the variable part of human antibodies.

D. In a positive indirect coombs test, antigen-antibody reaction happens in vivo.

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Question reproduced from IBO 2018, Theoretical Paper 2, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)