(A) Platelet-poor plasmas from 86 healthy donors (40 FXIIIVal/Val, 28 FXIIIVal/Leu, and 18 FXIIILeu/Leu) were reconstituted with washed platelets and O-negative red blood cells. Clotting was triggered with tissue factor and CaCl2, and contracted clots were weighed after 2 hours. Clot mass was normalized between assays performed on two different days. (B) Normalized clot mass. (C-F) Normalized clot mass were plotted as a function of (C) fibrinogen, (D) age, (E) FXIII activity, (F) prothrombin time, and (G) thrombin generation lag time. Lines indicate linear fits. Symbols are: FXIIIVal/Val (black closed circles), FXIIIVal/Leu (blue half-filled circles), and FXIIILeu/Leu (red open circles).