Direct Hospital Costs of Ambulatory versus Inpatient Needle-Localized Breast Biopsy: A Retrospective Cohort Study.

Introduction: As healthcare systems aim to optimize resource utilization, ambulatory breast surgery has been proposed as an alternative to inpatient care. However, data comparing direct hospital costs and identifying cost drivers for needle-localized breast biopsy (NLB) remain limited, particularly in low- and middle-income settings. Methods: This retrospective cohort study included adult patients who underwent NLB at a tertiary academic medical center between January 2020 and December 2024. Patients were classified as ambulatory (day surgery) or inpatient according to admission status. Total direct hospital costs were compared between groups, and multivariable linear regression was used to identify factors associated with increased cost. Costs were reported in Thai Baht (THB) and converted to U.S. dollars (USD) using an exchange rate of 1 USD = 33.82 THB. Results: A total of 392 patients were included, of whom 33 underwent ambulatory surgery and 359 underwent inpatient surgery. The ambulatory group was younger (47.9 ± 8.7 vs. 53.3 ± 10.5 years; Conclusions: Ambulatory NLB was associated with lower direct hospital costs than inpatient care in this single-center cohort. Admission status and operative time were associated with higher expenditure. These findings reflect real-world practice in selected patients; however, the observational design, marked group imbalance, and absence of safety events limit causal inference and preclude firm conclusions regarding comparative safety.