COLD AGGLUTININ ANTIBODIES

CLINICAL UTILITY:

Certain disease states are marked by the appearance of antibodies capable of agglutinating red blood cells at cold temperatures. These cold agglutinins are usually IgM class autoantibodies which recognize specific sites on red blood cells. They can be transiently associated with infections such as mycoplasma pneumonia and infectious mononucleosis, or be persistently present in diseases such as Waldenstrom’s macroglobulinemia, chronic lymphocytic leukemias, and idiopathic cold agglutinin disease. Post-infectious cold agglutinins are usually polyclonal, whereas cold agglutinins associated with B-cell neoplasms are generally monoclonal. The effects of cold agglutinins can range from minimal to severe hemolytic anemia. The degree of red blood cell destruction depends upon complex factors, including the titer of the antibody (greatest serum dilution able to agglutinate red cells) and the thermal amplitude (maximum temperature at which agglutination of red cells still occurs.) Generally, high titers occur with high thermal amplitudes. However, there are cases in which even low titers can be clinically significant if the reactive temperature is very high. If a cold agglutinin has a high thermal amplitude, special measures must be taken to keep the patient’s body temperature above the reaction temperature. In such cases, ordinary room temperature may trigger agglutination. Blood transfusions pose special problems unless the crossmatching has been done at 37°C. and the transfused cells have been washed to minimize the amount of complement in the transfusion.

The test for cold agglutinins has been used as a diagnostic check for mycoplasma pneumonia, since these antibodies are found in a significant percentage of patients, usually with titers greater than 1:64. The antibody begins to appear in the serum about ten days after the initial infection and reaches a maximum in about three weeks. The titers may not be high enough to produce overt hemolytic anemia, and usually disappear within three to four months. In cold agglutinin autoimmune hemolytic anemia, titers are usually 1:1000 or higher, even reaching 1:100,000. The serum of healthy individuals also contains a cold agglutinin which can react with red blood cells at temperatures used in laboratory tests (4°C.) Therefore, titers of 1:32 or less may be considered normal. Cold antibodies found in normal serum do not attach to red cells in vivo.

In lymphoreticular neoplasms associated with cold agglutinins the amount of antibody correlates with the amount of malignant tissue present, and often diminishes as the disease responds to treatment. Monoclonal cold agglutinins usually cause some degree of chronic hemolytic anemia. Chronic cold agglutinin disease usually occurs in patients over 55 years of age. To differentiate post-infection from malignant or idiopathic cold agglutinins, indicated especially in elderly patients, a Cold Agglutinin Identification may be ordered. Thermal amplitude tests are also available upon request.

METHOD DESCRIPTION:

The titer of cold agglutinins is quantitated using plasma, separated at 37°C., and agglutinated with red blood cells at 4°C. Agglutination is recorded at 4°C., and again after rewarming to 37°C. If agglutination disappears at 37°C. the highest titer showing agglutination at 4°C. is the reported result. For cold agglutination identification, the antibody is eluted from the patient’s red blood cells and tested by immunofixation for monoclonal antibody. For cold agglutinin thermal amplitudes in patients with cold agglutinins, the test is also carried out at warmer temperatures.

REFERENCE RANGE:

1:8 or less. No monoclonal component by immunofixation.

SPECIMEN REQUIREMENTS:

5 ml blood (EDTA) for Cold Agglutinin. 15 ml blood (EDTA) for Cold Agglutinin I.D. (immunofixation)