Cold-Reactive Autoantibodies - Detection:
Cold autoantibodies are defined as those that optimally bind to RBCs at temperatures below 37ºC. This typically occurs with carbohydrate antigens, which generate an exothermic reaction during antibody binding. Because carbohydrate antigens can generate a T-cell independent immune response that is not accompanied by class switching, most cold autoantibodies are of IgM class.
A cold-reactive autoantibody will therefore usually reveal itself as unexpected agglutination during ABO grouping, which is performed at room temperature; this agglutination will usually disperse if the sample is warmed to 37ºC.
Very potent cold agglutinins (i.e., those with high thermal amplitudes) may not completely dissociate upon warming, however, and variable reactions may therefore be seen during indirect antiglobulin testing:
- Mixed warm/cold autoantibodies: Occasionally, a warm-reactive autoantibody will be so potent that it will induce direct agglutination by immediate spin testing. Similarly, a very potent cold agglutin may cause panagglutination by IAT. Rarely, however, a patient will simultaneously exhibit both a cold-reactive and a warm-reactive antibody. Evidence would include the presence of panagglutinin in the eluate, reacting by IAT, combined with an agglutinin in the plasma that reacts strongest at cold temperatures.
Cold reactive autoantibodies typically bind to I/i or P antigens and, as with warm-reactive autoantibodies, treatment of reagent cells with proteolytic enzymes enhances the strength of reaction.
Next page: Confirmation