Idiopathic cold hemagglutinin syndrome (CHAD) is a disease of humans.
IgM binds to red blood cell surface antigens in the cold. This can occur in a susceptible individual as blood passes through cold extremities in cold weather. Complement is also fixed onto the RBC surface. Extravasular and intravascular haemolysis can occur. When blood returns the warm central circulation IgM can become detached from the RBCs leaving complement system components fixed on the RBC surface. This can influence Coombs test results. Hemoglobinuria can occur.
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