F11 and hyperinsulinemic hypoglycemia, familial, 4: Our result was confirmed with confocal fluorescence images and interestingly also indicates that the degree of FXI deficiency is important, since a severe FXI-deficient patient (<1 IU/dL) showed an impaired thrombus and fibrin formation when compared with a moderate FXI-deficient patient (6 IU/dL) and a control.