Fibrin network structure correlates with bleeding risk in FXI-deficient patients. Clots were formed from CTI-treated plasmas by recalcification and addition of tissue factor and phospholipids in the presence of AlexFluor488-conjugated fibrinogen. Clots were scanned with a Zeiss LSM700 confocal laser scanning microscope (Carl Zeiss, Inc, Thornwood, NY) with a 63× oil immersion pan-apochromatic lens.⁴²  Thirty optical sections (1024 × 1024 pixels) were collected at 0.36-μm intervals in the z-axis. Images were processed using 3-dimensional deconvolution algorithms (AutoQuant software × 3.0.1, Media Cybernetics Inc, Bethesda, MD). Fibrin network density analysis was performed as described in “Materials and methods.” (A) Representative confocal micrographs (z-projections of 30 individual slices) of plasma clots formed from a control individual and FXI-deficient nonbleeder and bleeder, as indicated. Images are 101.5 × 101.5 µm. (B) Fibrin network density (arbitrary units [A.U.]). Symbols represent plasmas from individual subjects; lines show median and interquartile range.