Sensing in Urinary Catheter Systems: From Measurands and Signal Fidelity to Supportable Clinical Claims

This review evaluates urinary catheter sensors designed to warn of crystalline encrustation and blockage or to monitor infection-related microbial, interfacial, and host-response states. A source-to-claim framework links each measured state and sampling compartment with its readout, reference endpoint, and supportable clinical claim. The analysis also considers whether catheter integration preserves the relationship between source, readout, and claim. pH-responsive systems have the strongest human feasibility evidence, although the studies are small, use different sampling configurations, and include few blockage events. Evidence for urease sensing is confined to analytical studies and controlled in vitro experiments. Mineral-deposition and hydraulic approaches rely mainly on catheter models or adjacent-device studies. Most infection-related platforms are sample-based assays, prototypes, or short-duration systems that measure clinically non-equivalent states. Analyte detection alone cannot establish a diagnosis or predict a later event in either application. Interpretation also changes with sensor location and with the effects of transport, fouling, and mechanical loading on the recognition interface. Translation requires validation over complete catheter episodes against an endpoint matched to the intended claim. An additional channel is warranted only if it resolves a prespecified uncertainty and improves clinically relevant performance against a fixed comparator.