PLAY
Cystatin C is a small protein produced at a constant rate by all nucleated cells and freely filtered by the kidneys, making it one of the most sensitive and reliable markers of glomerular filtration rate (GFR) — the key measure of kidney function. (source) Unlike creatinine, its levels are not significantly influenced by muscle mass, age, or diet, making it a more accurate kidney function marker across diverse body compositions.
For performance-focused individuals, kidney function directly impacts the clearance of metabolic waste, electrolyte regulation, and the body's ability to handle training-induced physiological stress. (source) Elevated cystatin C — indicating reduced kidney clearance — is associated with increased cardiovascular risk, systemic inflammation, and impaired recovery, all of which reduce performance ceiling over time.
