compatibility /kəmpat′əbil″itē/ [L, compatibilis, agreeable] , 1. the quality or state of existing together in harmony; congruity. 2. the orderly, efficient integration of the elements of one system with those of another. 3. the formation of a stable chemical or biochemical system, specifically in medication, so that two or more drugs can be administered at the same time without producing undesired side effects or without canceling or affecting the therapeutic effects of the others. 4. (in immunology) the degree to which the body’s defense system tolerates the presence of foreign material, such as transfused blood, grafted tissue, or transplanted organs, without an immune reaction. Usually identical twins are completely compatible. 5. (in blood grouping or crossmatching) the lack of reaction between blood groups so that there is no agglutination when the red blood cells of one sample are mixed with the serum of another sample; no reaction from transfused blood. −compatible, adj.
