This technology includes a clinical diagnostic tool for measuring vitamin C elimination by human kidneys that can be used for detecting, monitoring, and managing acute and chronic diseases. Findings revealed significant associations between vitamin C renal leak status and clinical variables affecting renal function and blood glucose. The technology uses vitamin C depletion-repletion kinetics and pharmacokinetic models to establish a physiological vitamin C renal threshold. This allowed us to define “vitamin C renal leak” as urinary vitamin C levels below the established minimal elimination threshold. The technology was tested and validated in multiple clinical studies involving more than five cohorts of healthy controls or those with chronic disease.