Extracorporeal circuit clotting in hemodialysis: incidence and associated factors in real-world practice

Background and hypothesis: Extracorporeal circuit (ECC) clotting during hemodialysis (HD) compromises dialysis efficacy, increases workload, and jeopardizes patient safety. However, in routine clinical practice, ECC performance is influenced by the interaction of patient-related, technical, and pharmacological factors that are rarely evaluated simultaneously in large multicentre cohorts. Methods: We conducted a multicentre retrospective observational study including all consecutive HD sessions performed across 15 hemodialysis units of Fundación Renal Española between January 1, 2023 and February 15, 2024. Recorded variables included anticoagulation type and dose, dialysis modality (high-flux HD or online HDF), vascular access, dialyzer surface area, session duration, and dialysis adequacy (KT). ECC clotting was assessed at the end of each session using a standardized visual grading scale. Associations were explored using unadjusted analyses, multivariable logistic regression adjusted for dialysis centre, and a patient-level generalized linear mixed model. Results: A total of 186,637 HD sessions were analysed. ECC clotting was infrequent: 96.3% of sessions showed no or minimal clotting, 1.8% partial clotting, and 2.0% complete clotting. Sessions complicated by ECC clotting delivered a lower dialysis dose (mean KT 49.5 ± 11.1 vs 52.2 ± 10.1; p 2.0 m² were independently associated with increased clotting risk, whereas LMWH and postdilution HDF were associated with lower risk. Substantial inter-individual variability in clotting risk was observed at the patient level. Conclusion: Although ECC clotting during HD was infrequent, it had a clear negative impact on dialysis delivery and was consistently associated with identifiable and potentially modifiable factors. Catheter-based access, lack of anticoagulation, and larger dialyzer surface area were the strongest determinants of clotting risk. The marked patient-level variability underscores the need for individualized anticoagulation and dialysis prescriptions to optimize circuit patency, dialysis adequacy, and patient safety in routine clinical practice.