Proposed BDUC diagnostic algorithm. *Level 2 laboratory testing performed in patients with abnormal ISTH BAT scores but normal level 1 tests. **Level 3 laboratory testing is reserved for patients with normal level 2 testing but marked bleeding phenotypes (eg, IATH BAT >10 or recurrent anemia or strong family histories or planned procedures associated with major bleeding risks). Ideally, these level 3 tests should be performed in the context of a research study.