Thermal amplitude is a test to determine the highest temperature the antibody will bind to the antigen. This, along with cold agglutinin titer, helps to determine the clinical significance of the cold autoantibody. Thermal amplitude can be used as a guide for surgical procedures that need to lower the body temperature. This is commonly done in cardiac procedures. The thermal amplitude procedure will determine how far down they can bring the patient's temperature before the cold agglutinin starts reacting. Antibody screens using the patient's plasma and donor RBCs are performed at 4ºC, 22ºC, 30ºC, and 37ºC for 1 hour and observed for agglutination.
A thermal amplitude >30ºC is considered clinically significant and associated with potential accelerated RBC destruction. Normal patients will often have agglutination seen at 4ºC. However, in patients with CAD, the agglutination continues on to 30ºC or higher.
