Autoantibodies with specificity against RBC determinants that react at low temperature but not at body temperature. (Reactions against i determinants are less common.) The cold-reactive agglutinins are of the IgM class immunoglobulins; very rarely IgG. The IgM autoantibodies bind at low temperature to complement on the RBC membrane.
Normal titer: <1:32 (negative result).
Use
Hemolytic anemia, particularly in the presence of lymphoproliferative disorders
When the clinical symptomatology suggests cold agglutinin disease
Interpretation
Cold agglutinin titers above 1:32 are diagnostic for the presence of cold agglutinin disease. The titer in affected patients may be >1,000.
Limitations
Blood must be collected, clotted, and the serum separated at 37 ‚ °C, and in addition, the sample must be maintained at 37 ‚ °C. Alternatively, it can be collected on EDTA at room temperature, but then, it must be warmed for at least 15 minutes at 37 ‚ °C.
The direct (Coombs) antiglobulin test is positive against C3d and C4d components of complement.
Low levels may also found in healthy individuals and those with peripheral vascular disease or nonlymphoid neoplasm.
Cold-reacting autoantibodies are mostly IgM, occasionally IgG, and rarely IgA. May be polyclonal, also can be monoclonal usually with kappa light chain.
Refrigeration of blood at any time adversely affects the results, as does severely hemolyzed or lipemic specimens.