(1) APPT: "inconsistent" prolongation of APPT occurs; lengthening depends on levels of factor VIII present and on the sensitivity to factor VIII of the reagent being used.
(2) Mixing test: Prolongation of APPT is corrected by mixing the patient's plasma in equal parts with a pool of normal plasma.
(3) BT: bleeding time (Ivy method) is only increased in around 50% of cases; it is never increased in type 2N von Willebrand disease; in vitro tests to reproduce bleeding time can provide diagnosis (except in type 2N von Willebrand disease).
(4) Platelet count: this parameter is normal in most forms of von Willebrand disease. The platelet count may be depressed in some patients with type 2B von Willebrand disease, in whom fluctuating thrombocytopenia of varying severity may be seen.