ned. Objective: To characterize the bleeding phenotype, treatment patterns, and diagnostic distribution of IPFDs across the United States using the national ATHNdataset. Methods: We conducted a retrospective cohort study using the ATHNdataset, a deidentified registry maintained by the American Thrombosis and Hemostasis Network. Clinical outcomes, including bleeding events, laboratory data, treatments, and procedures, were analyzed for participants with IPFDs between 2013 and 2022 and with active follow-up from January 2021 to December 2022. Results: Among 2302 individuals with IPFDs, 8.1% as GT, 2.4% as BSS, 7.0% as granule defects, and 81.6% as IPFD-other. Among 985 participants with active follow-up, 236 bleeding events were reported across 251 patients. The most common events were epistaxis (42.8%), followed by soft tissue (14.4%) and oral bleeding (13.9%). Notably, intracranial hemorrhage occurred in 8 patients and joint bleeds in 82, reflecting significant morbidity across all subtypes. Median ISTH-BAT scores were elevated—13 in GT, 16 in dense-granule defects, and 7 in unclassified IPFDs—exceeding reported population norms. Regarding hemostatic management, antifibrinolytics were used in over half of all patients, with desmopressin and platelet transfusions being used less frequently. Conclusion: By defining the clinical spectrum, treatment utilization, and residual diagnostic uncertainty across IPFDs, this study underscores the importance of improving diagnostic precision and care for patients with platelet function disorders in the modern era....