SID : A new carbohydrate blood group system based on a well-characterized but still mysterious antigen of great pathophysiologic interest
The high-prevalence blood group antigen, Sda, had been puzzling blood bankers and transfusionists for at least a decade when it was reported in 1967. The characteristic mix of agglutinates and free red blood cells (RBCs), caused by anti-Sda, is seen with the RBCs from 90 percent of individuals of European descent. However, only 2-4 percent of individuals are truly Sd(a-) and may produce anti-Sda.
