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Isoagglutinins are antibodies produced by an individual that cause agglutination of RBCs in other individuals. People possess isoagglutinins directed toward the A or B antigen absent from their own RBCs. For example, type B or O individuals will usually possess anti-A. The anti-A is formed in response to exposure to A-like antigenic structures found in ubiquitous non-red cell biologic entities (eg, bacteria).
Isoagglutinins present in the newborn are passively acquired from maternal circulation. Such passively acquired isoagglutinins will gradually disappear, and the infant will begin to produce isoagglutinins at 3 to 6 months of age.
Isoagglutinin production may vary in patients with certain pathologic conditions. Decreased levels of isoagglutinins may be seen in patients with acquired and congenital hypogammaglobulinemia and agammaglobulinemia. Some individuals with roundworm infections will have elevated levels of anti-A.
Evaluation of individuals with possible hypogammaglobulinemia
Investigation of suspected roundworm infections
The result is reported as antiglobulin phase, in general representing IgG antibody. The result is the reciprocal of the highest dilution up to 1:2048 at which macroscopic agglutination (1+) is observed. Dilutions >1:2048 are reported as >2048.
Decreased isoagglutinin titers may be seen in normal elderly individuals and in children < or =12 months.
This test is not useful for individuals with blood type A or AB.
Interpretation depends on clinical setting.
Technical Manual. 15th edition. Arlington, VA, American Association of Blood Banks, 2005