define cold agglutinin
Cold agglutinins are antibodies that cause clumping or agglutination of RBCs at cold temperatures in individuals with certain conditions or who are infected by particular organisms. Cold agglutinins are associated with Mycoplasma pneumoniae infection. M. pneumoniae has i antigen specificity to human RBC membranes. Fetal cells largely contain i antigens, but by 18 mo most cells carry the I antigen.