The most common hereditary disorder of hemostasis is von Willebrand disease (VWD) The most common hereditary coagulation disorders are The hemophilias Testing of Coagulation Disorders Patients in whom a coagulation disorder is suspected require laboratory evaluation beginning with Prothrombin time (PT) and partial thromboplastin time (PTT) Complete blood count (CBC) with platelet count Peripheral blood smear Results of these tests narrow the diagnostic possibilities and guide further testing.