Cost-Stirling, COST, is considered a collection of red cell antigens rather than a blood group system. There are two main antigens in the COST collection (ISBT 205), Csa and Csb, which are antithetical antigens. Csa is found in approximately 98% of the population and Csb is found in approximately 35%. COST antigens were previously believed to be Knops system antigens, but were discovered to have no association with the CR1 protein and were re-classified accordingly.
Disease Association
Antibodies to COST collection antigens are not known to be clinically significant and have no known disease associations.
Treatment
They are resistant to all common chemical, enzyme, and acid treatments so when trying to resolve a suspected anti-Csa, a rare red cell negative for the antigen is typically necessary as it does not adsorb well due to its low avidity.
