universal donor u·ni·ver·sal donor (yōō'nə-vûr'səl)
A person whose red blood cells do not contain agglutinogen A or B and are therefore not agglutinated by plasma containing either of the ordinary isoagglutinins, alpha or beta; a person who has group O blood.
A person who has group O blood and is therefore able to serve as a donor to a person with any other blood type. Group O blood contains red blood cells that do not have the antigen A or B and thus do not react with antibodies to these antigens found in the plasma of the other blood types. See also blood type.