Longitudinal monitoring of antibodies against FVIII in a patient with acquired hemophilia A. Presented are the results of a longitudinal monitoring of antibodies against FVIII, including titers of binding antibodies, differentiated for individual immunoglobulin isotypes and IgG subclasses (A); Bethesda titers of FVIII inhibitors (A-B); and apparent affinities of antibodies, differentiated for individual immunoglobulin isotypes and IgG subclasses (B). Antibody data for IgM, IgA, IgG2, and IgG3 were below the cutoff of the antibody assays and are, therefore, not shown. Data for titers of antibodies against FVIII include the variation of the method (±1 titer step). Data for apparent affinity include the 95% CI. Presented are Bethesda titers of FVIII inhibitors (BU/mL; filled red diamonds); titers of antibodies against FVIII (IgG1 [open blue circles] and IgG4 [open green diamonds]); and apparent affinities of FVIII-specific antibody clusters for IgG1 (filled blue bars) and IgG4 (filled green bars). The details of the medical history for this patient are included in the supplemental Data, Online Supplement 2.