Correlation between titers of FVIII-binding antibodies and inhibitor titers in hemophilia A patients with inhibitors (HA-INH). The correlation between titers of FVIII-binding antibodies and inhibitor titers in hemophilia A patients with inhibitors was determined for the IgG subclasses (A) IgG1, (B) IgG2, (C) IgG3, (D) IgG4 using the 2-tailed nonparametric correlation according to Spearman, and calculated using GraphPad Prism 5 Software. The correlation coefficient (r) is given for each IgG subclass; 95% confidence intervals are indicated in parentheses when the correlation is significant (*P ≤ .05). The correlation between titers of IgA and IgM FVIII-binding antibodies and inhibitor titers was not done because of the low number of FVIII-binding IgA and IgM antibodies detected in hemophilia A patients with inhibitors. The dotted line at a titer of 1:80 indicates the minimum titer required for proof of specificity. Titers of < 1:80 were too low to be confirmed for specificity. n.s. indicates not significant; and ND, not detectable.