The weekend effect in spontaneous tumor lysis syndrome in patients with hematological malignancy: National trends in dialysis utilization, mortality, and resource use in the United States.

e18632 Background: Spontaneous tumor lysis syndrome (sTLS) is a rare but highly lethal oncologic emergency. Whether outcomes differ by admission timing and the unavailability of oncological and nephrological consultation remains unknown. We evaluated the association between weekend admission and clinical outcomes among patients hospitalized with sTLS. Methods: We conducted a retrospective analysis of the all-payer inpatient database from the Healthcare Cost and Utilization Project (HCUP) from 2018 to 2021. We included adult, non-elective hospitalizations with TLS and hematologic malignancy and excluded admissions involving recent cancer-directed therapy. Weekend versus weekday admission was the primary exposure. Primary outcomes were in-hospital mortality and dialysis utilization. Secondary outcomes included acute kidney injury (AKI), markers of critical illness, length of stay, and total hospital charges. Survey-weighted multivariable regression models were used to report odds ratios while adjusting for demographic, socioeconomic, comorbidity, and illness-severity factors. Sensitivity analyses were performed excluding AKI. Results: The final cohort included 6,950 hospitalizations, of which 21.7% occurred on weekends. Overall, in-hospital mortality was high 29.9%, and 10.7% of patients required dialysis. Weekend admission was independently associated with higher in-hospital mortality compared with weekday admission (adjusted OR 1.16, 95% CI 1.01–1.34, p=0.047), but not with dialysis utilization (adjusted OR 0.89, 95% CI 0.74–1.05). Dialysis use, mortality, length of stay, and hospital charges were primarily driven by illness severity, including AKI, mechanical ventilation, vasopressor use, and comorbidity burden. Conclusions: Among patients hospitalized with spontaneous TLS, weekend admission is associated with increased mortality but not increased dialysis use. These findings suggest a clinically meaningful weekend effect in this high-risk population and highlight the need for consistent, timely management of sTLS across admission days.