Standardisation of Definition and Management for Bleeding Disorder of Unknown Cause: Communication from the SSC of the ISTH.

In many patients referred with significant bleeding phenotype, laboratory testing fails to define any hemostatic abnormalities. Clinical practise with respect to diagnosis and management of this patient cohort poses significant clinical challenges. We recommend that bleeding history in these patients should be objectively assessed using the ISTH bleeding assessment tool (BAT). Patients with increased BAT scores should progress to hemostasis laboratory testing. To diagnose BDUC, normal complete blood count, prothrombin time, activated partial thromboplastin time, thrombin time, von Willebrand factor antigen, von Willebrand factor function; coagulation factors VIII, IX and XI and platelet light transmission aggregometry (LTA) should be the minimum laboratory assessment. In some laboratories, additional specialized haemostasis testing may be performed and identify other rare causes of bleeding. We recommend that patients with a significant bleeding phenotype but normal laboratory investigations should be registered with a diagnosis of 'Bleeding disorder of unknown cause (BDUC)' in preference to other terminology. Global haemostatic tests and markers of fibrinolysis demonstrate variable abnormalities, and their clinical significance remains uncertain. Targeted genomic sequencing examining candidate hemostatic genes has a low diagnostic yield. Underlying BDUC should be considered in patients with heavy menstrual bleeding since delays in diagnosis often extend to many years and negatively impact quality of life. Treatment options for BDUC patients include tranexamic acid, desmopressin and platelet transfusions.