Coexistence of Cold Agglutinin and Cryoglobulin in a Patient With Severe Anemia Following COVID-19 Infection

We report a case of coexisting cold agglutinin and cryoglobulin in a patient with severe anemia following COVID-19 infection, in whom direct antiglobulin testing revealed C3d positivity and immunoglobulin G negativity. There was no evident hemolytic anemia, thrombosis, or clinically significant IgM monoclonal gammopathy. The anemia improved with folic acid supplementation alone accompanied by a decrease of the cold agglutination titer, and the direct antiglobulin test became negative. Despite continuous positivity for cryoglobulinemia, the patient exhibited no clinical symptoms such as thrombosis. Immunosuppressive therapy for cold-related hematologic disorders after COVID-19 infection should be considered carefully.