Cold agglutinins (CAs) are a type of red cell autoantibody, mostly comprised of IgM and a few IgG and IgA. 1 At temperatures below 31°C, these antibodies easily combine with I, i, or SP1 antigens on red cells, resulting in red cell agglutination and microcirculation blockage, which could cause cyanosis and even autoimmune hemolytic anemia (AIHA) in more severe cases. 2 AIHA caused by CAs can be divided into two types: cold agglutinin disease (CAD) and cold agglutinin syndrome (CAS). The former is B-cell clonal lymphoproliferative disorder (LPD); the latter is commonly seen in mycoplasma pneumonia, infectious mononucleosis, and lymphoma. [2][3][4] High concentrations of CA can induce erythrocyte agglutination, which has a great impact on complete blood count (CBC) results. In
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