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Cold agglutinins are nonspecific IgM antibodies which agglutinate red blood cells at cold temperatures between 0 and 30oC. In the past, cold agglutinin titers were often used as a surrogate test for Mycoplasma pneumonia, since mycoplasma infections are often associated with elevated anti-I titers. Numerous conditions besides Mycoplasma pneumonia will give an elevated titer including: viral infections, hemolytic anemia, liver disease and pregnancy. More specific mycoplasma IgG and IgM immunoassays are preferred to diagnose Mycoplasma. pneumonia. Cold agglutinin titers should only be ordered to diagnose cold autoimmune hemolytic anemia. Cold agglutinins are present in 95% of healthy patients at titers < 1:16. Titers less than 1:32 are considered negative. The best prediction of the biological activity of cold autoantibodies is thermal amplitude. Harmless cold autoantibodies react with RBCs up to a temperature of 10 to 15 degrees C in vitro, while antibodies with potentially harmful effects react in vitro at 30 degrees C or higher. Specimen requirement is one 10 mL SST tube of blood. The tube should be immediately placed in a 37 C water bath and allowed to clot. After 10 minutes, the tube can be centrifuged and the serum transported to the laboratory at ambient temperature. If a water bath is not available, the tube should be transported at ambient temperature without centrifugation. |
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