Abstract
<title>Abstract</title> <p>Background Geographic accessibility is a structural determinant of equitable transplantation, yet national assessments rarely integrate graft-specific biologically defined transport constraints with high-resolution population modeling. In this study, population exposure to clinically relevant travel-time thresholds for multiple transplant modalities in Colombia was quantified, and demographically consequential underserved zones were identified. Methods A cross-sectional national geospatial analysis was conducted using a harmonized 100 m population grid derived from census-based projections. All licensed transplant-capable facilities operational as of September 30, 2025, were geocoded and validated. Road-based travel-time surfaces were generated using least-cost path modeling under class-specific regulatory speed assumptions. Travel times were categorized using graft-specific clinically acceptable thresholds reflecting ischemic tolerance. Underserved zones for service expansion were identified by combining threshold exceedance with a ≥ 100,000-inhabitant criterion and spatial coherence filtering. Results Accessibility varied substantially across modalities. The population beyond clinically acceptable thresholds was highest for cardiac valves (58.9%), heart (45.6%), lung (39.2%), and bone tissue (31.7%). Approximately 3.0% of the national population resided in areas not connected to the motorized road network under model assumptions and were analyzed separately. Demographically viable underserved zones were most numerous for cardiac valves (34), heart (30), and lung (26), which clustered predominantly in northern and southwestern Colombia. Conclusion In Colombia, transplant access inequities are modality dependent and reflect interactions among graft-specific time constraints, service centralization, and transport connectivity. Threshold-anchored geospatial modeling provides a reproducible framework for equity-oriented transplant planning across the Americas and globally.</p>