Changes in factor VIII binding capacity of von Willebrand factor and factor VIII coagulant activity in two patients with type 2N von Willebrand disease after hemostatic treatment and during pregnancy.

The changes of the FVIII binding capacity of vWF after the infusion of FVIII/vWF concentrate was studied in two patients with type 2N vWD, and also during pregnancy in one of them. After infusion of FVIII or DDAVP to the patients, FVIII:C in plasma increased as expected, but it then decreased, with a markedly short half-life, of about 2 h, due to the defect in the FVIII binding capacity of vWF in plasma. However, after infusion of FVIII/vWF concentrate (40 U of FVIII:C/kg), FVIII:C increased, from 4-6 to 100-160 U/dl, more than the expected values, and decreased with the half-life expected. The FVIII binding capacity of vWF in plasma changed in parallel with the concentration of exogenous normal vWF, with a half-life of more than 24 h. During pregnancy, no increase of FVIII:C was observed, although vWF:Ag increased from 40 (before pregnancy) to 90 U/dl in plasma at 35th week of gestation. The FVIII binding capacity of vWF in plasma showed no increase during pregnancy. Accordingly, the administration of FVIII/vWF concentrate to the patient at delivery resulted in adequate hemostasis.