Plasma or urinary clearance of exogenous filtration markers is required for assessment of measured glomerular filtration rate. Although multiple methods are available, none is widely used because of their complexity, each has measurement error, and standardization is limited. Recently, a study validated the plasma clearance of a new exogenous filtration marker, relmapirazin, which can be detected by its transdermal fluorescence, potentially simplifying the procedure and increasing access to measured glomerular filtration rate.