Cystatin C

Cystatin C is a low-molecular-weight cysteine protease inhibitor produced at a constant rate by all nucleated cells and freely filtered by the glomerulus, making it a more sensitive and muscle-mass-independent marker of glomerular filtration rate (GFR) than creatinine. Salivary cystatin C is detectable via proteomics and reflects both local oral tissue production and systemic transudation, providing a non-invasive index of renal functional reserve and hydration-dependent filtration changes during exercise. Dharnidharka et al. (2002) and Levey et al. (1999) established cystatin C as a superior GFR marker particularly valuable in athletes where creatinine is confounded by high muscle mass.