an autoantibody of the IgG class responsible for paroxysmal cold hemoglobinuria; it is adsorbed to erythrocytes only at temperatures of 20°C or lower, causing the erythrocytes to lyse in the presence of complement at higher temperatures; it has a specificity within the blood group P; it is also occasionally present for short periods of time following measles and other infections, and formerly was frequently associated with syphilis. SYN: cold hemolysin.
