Which of the following is NOT indicative of von Willebrand's disease?

Von Willebrand's disease is primarily characterized by a deficiency or dysfunction of von Willebrand factor (vWF), which plays a crucial role in platelet adhesion and the stabilization of factor VIII in the coagulation cascade. Among the key laboratory findings in this condition, a decreased level of factor VIII (VIII:C) is often observed due to the unstable association of factor VIII with vWF.

The presence of decreased VIIIR:Co (von Willebrand factor activity) is also indicative of the disease, as this reflects the functional aspect of vWF in facilitating platelet aggregation. A prolonged bleeding time is characteristic of von Willebrand's disease due to impaired platelet function and adhesion.

In contrast, a decreased platelet count is not a typical finding in von Willebrand's disease. Patients usually have normal platelet counts, as the issue lies more in the function of the platelets and their interaction with von Willebrand factor rather than in their overall quantity. Thus, selecting a decreased platelet count as not indicative of von Willebrand's disease aligns with the understanding that this condition is not associated with thrombocytopenia.