A prototype medical device for trans-cutaneous monitoring of kidney function has been developed, validated, and used in a clinical trial on 16 healthy subjects having a wide range of skin color types. The fluorescent tracer agent MB-102 was administered intravenously as a bolus that was varied between 0.5 and 4 μmole/kg subject weight. The tracer agent was tracked as a function of time in plasma by blood sampling and trans-cutaneously at four body sites (sternum, forehead, arm, and side) simultaneously. Excitation was performed with a very low level of amplitude-modulated LED light at 450 nm (<50 μW/cm2), and fluorescence emission was synchronously detected at 570 nm. With adjustment of detection gain between subjects, no skin color dependence was observed of the signal-to-noise ratio (SNR) of the transcutaneous measurements. The primary source of measurement noise appeared to be subject motion, likely due to variations in blood content at the skin measurement site. A typical two-compartment pharmacokinetic dependence was observed with equilibration of the fluorescent agent between the vascular space into which it was injected and the extracellular space into which it subsequently diffused. Variation of this equilibration time was observed across body sites, with the sternum providing the shortest and most consistent equilibration. After equilibration, the terminal fluorescence time dependence at the sternum site was found to be highly correlated with tracer agent concentration time dependence sampled from the blood plasma.