The S and s antigens form part of the MNS blood grouping system and were reported in 1947 and 1951 respectively. Anti-S and Anti-s have been implemented in immediate and delayed Haemolytic Transfusion reactions and Haemolytic Disease in the new born. Indirect agglutination of red cells that carry the S – antigen or s-antigen occurs in the antiglobulin phase.  In the absence of the S- antigen or s-antigen, no indirect agglutination is generally observed.

The Biorex Diagnostics Anti-S and Anti-s reagents consist of human monoclonal IgG antibodies diluted in phosphate buffer containing sodium chloride and bovine albumin. The reagent requires no further dilution or addition for recommended techniques.