Kashani, Kianoush

The glomerular filtration rate (GFR) is a key indicator of kidney function, yet no ideal method exists for its direct measurement. This two-part review examines the development of GFR measurement techniques, focusing on their physiologic basis, performance characteristics, and clinical applications. Part 1 reviews endogenous markers used to estimate GFR (eGFR), including creatinine- and cystatin C-based equations, with emphasis on their derivation, limitations, and clinical use. Part 2 addresses exogenous filtration markers and measured GFR (mGFR) methodologies, highlighting comparative performance and specific uses. Emphasis is placed on innovation in marker development, highlighting the need for continued development and standardization to enhance accuracy and clinical utility.

Measured glomerular filtration rate (mGFR) remains the reference standard for precise assessment of kidney function when estimated approaches are insufficient. This second part of a two-part series reviews exogenous filtration markers used to obtain mGFR, including inulin, iothalamate, iohexol, and radionuclide-based tracers, with emphasis on their physiologic handling, analytic methods, accuracy, and clinical applicability. The review further examines emerging fluorescent and near-infrared tracers coupled with transcutaneous monitoring technologies that enable rapid or continuous assessment of GFR. Together, these approaches illustrate the evolution of mGFR measurement toward methods that are more practical, scalable, and responsive to dynamic changes in kidney function, while maintaining analytical accuracy.