Thermal range (also called “thermal amplitude”) refers to the temperature range over which a blood group antibody effectively causes increased destruction of red blood cells carrying its target antigen. Laboratories may check the thermal range of a cold-reacting alloantibody or autoantibody in order to assess the likelihood that it may cause hemolysis. Since cold antibodies, by definition, enjoy interactions with RBCs at cold temperatures (0-4C), the question is really: “How warm can it get before the antibody stops reacting?” The closer to body temperature (37C) the antibody reacts, in general, the more likely it is to be clinically significant (especially when that range includes reactivity at 30C or higher). Antibodies with a low thermal range, with reactivity only below 30C, are unlikely to cause significant harm to target red blood cells in the body.