Comparison of FXI:C levels and APTT results among controls, bleeders, and nonbleeders in FXI deficiency. Comparison of FXI:C levels (A) and APTT results (B) in control individuals (n = 50), nonbleeder FXI-deficient (n = 50), and bleeder FXI-deficient (n = 24) groups. Line and error bars represent mean ± standard deviation. ROC curve analysis to test the ability of FXI:C (C) and APTT (D) assays to identify bleeders from nonbleeders in FXI deficiency. *Specificity of test at 100% sensitivity.