Test ID: BTR    
Isoagglutinin Titer, Anti-B, Serum

Useful For Suggests clinical disorders or settings where the test may be helpful

Evaluation of individuals with possible hypogammaglobulinemia

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Isoagglutinins are antibodies produced by an individual that cause agglutination of red blood cells (RBC) in other individuals. People possess isoagglutinins directed toward the A or B antigen absent from their own RBC. For example, type A or O individuals will usually possess anti-B. The anti-B is formed in response to exposure to B-like antigenic structures found in ubiquitous non-red blood 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.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Interpretation depends on clinical setting. No defined reference values.

Interpretation Provides information to assist in interpretation of the test results

The result is reported as antiglobulin phase, in general representing IgG antibody. The result is the reciprocal of the highest dilution up to 1:1024 at which macroscopic agglutination (1+) is observed. Dilutions above 1:1024 are reported as greater than 1024.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Decreased isoagglutinin titers may be seen in normal elderly individuals and in children 12 months or younger.


This test will not be performed for individuals with blood type B or AB.

Clinical Reference Recommendations for in-depth reading of a clinical nature

Fung MK, Eder AF, Spitalnik SL, Westhoff CM: Technical Manual. 19th ed. AABB; 2017