The Safety of Pre-Filter Heparin for Circuit Clotting Prevention in Continuous Renal Replacement Therapy: A Retrospective Evaluation.

Background: Circuit clotting is a common complication of continuous renal replacement therapy (CRRT). Pre-filter unfractionated heparin (UFH) is widely used to maintain circuit patency, but real-world data describing its safety and efficacy are limited. Methods: This retrospective, single-health-system study evaluated critically ill adults receiving pre-filter UFH for CRRT clotting prevention between 2021 and 2025. The primary outcome was clinically relevant major bleeding, adapted from International Society on Thrombosis and Haemostasis criteria. Secondary outcomes included pre-filter UFH dosing and monitoring patterns and CRRT filter outcomes. Categorical and continuous variables were summarized descriptively. Associations with bleeding were explored using Fisher's exact tests. The times to bleeding and filter failure were evaluated using Kaplan-Meier analyses. Results: Of 96 screened patients, 77 met the inclusion criteria. Clinically relevant major bleeding occurred in 18 patients (23%), with no characteristics significantly associated with bleeding. The cumulative probabilities of bleeding at 24, 48, 72, and 96 h were 1.3%, 8.4%, 23.8%, and 35.3%, respectively. The median pre-filter UFH treatment duration was 72 h (IQR 37-137). Fifty-one patients (66%) experienced CRRT filter failure, with a median time to first filter failure of 36 h (95% CI 26.8-51.3). Conclusions: Clinically relevant major bleeding and filter failure were common during pre-filter UFH therapy in this cohort. Bleeding continued to occur with longer pre-filter UFH exposure, supporting close monitoring for bleeding during prolonged therapy. These findings provide real-world characterization of pre-filter UFH use but do not establish comparative safety. Larger prospective studies are needed to optimize pre-filter UFH dosing and monitoring.