VWF and Von Willebrand disease: A noteworthy point is that patients with von Willebrand disease may also present with an isolated prolonged aPTT because of the reduced factor VIII causing the aPTT prolongation.14 Factor VIII levels may be reduced in patients with von Willebrand disease because von Willebrand factor protects factor VIII from proteolysis.15 Therefore, workup for von Willebrand disease may be appropriate for patients with both isolated prolonged aPTT and reduced factor VIII; however, aPTT is not a reliable test in screening for a diagnosis of von Willebrand disease.16