AIHA cannot be attributed to any single autoantibody. To determine the autoantibody or autoantibodies present in a patient, the Coombs test, also known as the antiglobulin test, is performed. There are two types of Coombs tests, direct and indirect; more commonly, the direct antiglobulin test (DAT) is used. Classification of the antibodies is based on their activity at different temperatures and their etiology. Antibodies with high activity at physiological temperature (approximately 37 °C) are termed warm autoantibodies. Cold autoantibodies act best at temperatures of 0–4 °C. Patients with cold-type AIHA, therefore, have higher disease activity when body temperature falls into a hypothermic state. Usually, the antibody becomes active when it reaches the limbs, at which point it opsonizes RBCs. When these RBCs return to central regions, they are damaged by complement. Patients may present with one or both types of autoantibodies; if both are present, the disease is termed "mixed-type" AIHA.