Improved risk stratification and early detection of disease is a broad, unmet need in clinical medicine. Despite substantial biomarker research, success has been limited partly because biomarkers are typically studied in a "static" paradigm, with one-time measurements. We envision that the ability to measure biomarkers daily at home, providing information on dynamic changes within an individual over time, would substantially increase the sensitivity as well as specificity of biomarkers, especially for kidney and urologic diseases. In the proposed project we will use both theoretical and empirical approaches to create novel paper-based microfluidic devices to quantify red blood cells in urine, as a potential recurrence screening approach in bladder cancer patients. The devices will be developed by patterning “omniphiliic” channels on top of “omniphobic” paper, enabling robust size-based separation and analysis of cells at low cost.