2017 Volume 54 Issue 5 Pages 433-437
Direct Coombs test (DAT)-negative autoimmune hemolytic anemia (AIHA) accounts for approximately 10% of AIHA cases. Low-affinity IgG may contribute to the negative test results. We report the case of a girl aged 4 years and 1 month with severe anemia [hemoglobin (Hb) level, 5.3 mg/dL], suspected of having DAT-negative AIHA owing to low-affinity IgG. Although suspected of having AIHA, her laboratory examinations by the DAT-tube method revealed a negative DAT result. Because her Hb level improved after steroid therapy, she was diagnosed as having DAT-negative AIHA. Her Hb level was dependent on the steroid dose. Rituximab was administered 6 months postadmission. Thereafter, she showed partial improvement and treatment was discontinued 5 years after diagnosis. Her test sample collected at diagnosis and stored under chilled conditions for several days showed DAT C3bC3d positivity. Five years after the disease onset, DAT by the column method revealed IgG positivity. This method did not require RBC washing; in fact, IgG level decreased after RBC washing, suggesting the presence of low-affinity autoantibodies.
