Unusual suppression of Kell system antigens in a healthy blood donor.

Red cells of a Kp(a+) donor, ascertained as a result of screening donor red cell units with anti-Kpa, reacted only very weakly with anti-Kpb and demonstrated weakened expression of various other Kell and para-Kell antigens. Family studies revealed a Kp(a+) sister with similarly weakened expression of Kpb and other Kell and para-Kell antigens. Red cell morphology was normal in both of these individuals. This phenotype is different from any previously reported and is named the Allen phenotype.