A 26-year-old woman presents with fatigue and jaundice. Hemoglobin is 7.5 g/dL, reticulocytes are elevated, and spherocytes are seen on peripheral smear. The direct antiglobulin (Coombs) test is positive with anti-IgG reagent alone. Which finding best fits this result?

• A IgM antibodies bound to red cells fixing complement, typical of Mycoplasma infection
• B Drug-induced immune complexes deposited on the red cell surface
• C Maternal anti-D antibodies crossing the placenta onto fetal red cells
• D Warm-reactive IgG autoantibodies coating the red cells without bound complement ✓

Explanation

A direct Coombs test positive only with anti-IgG indicates warm autoimmune hemolytic anemia, in which opsonized IgG-coated red cells are cleared extravascularly by splenic macrophages, producing spherocytes. Cold agglutinin disease gives a positive test with anti-C3 (complement) rather than anti-IgG alone. Maternal anti-B would be detected in the infant's sample, not the mother's.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.