Creatinine

Creatinine is a muscle-metabolism byproduct filtered by the kidneys, and the number used — alongside age and sex — to estimate eGFR.

Reference range

Male: 0.7–1.3 mg/dL (optimal ≤ 1.2 mg/dL)
Female: 0.6–1.1 mg/dL (optimal ≤ 1.1 mg/dL)

Watch points

Critical: at or above 2 mg/dL
High: at or above 1.5 mg/dL

Same thresholds apply to men and women in this table.

Why hard-training athletes watch it

Higher muscle mass alone raises baseline creatinine independent of kidney function — a lean, heavily-muscled lifter can show a 'high' reading on a scale calibrated for the general population, which is exactly why eGFR (not creatinine alone) is the number to watch.

When to retest

Stay well-hydrated before the draw and skip a very high-protein meal or intense training in the 24 hours prior — both can transiently raise this number.

Talk to your clinician

Stay well hydrated and discuss kidney function with your clinician — note muscle mass can raise creatinine. A muscular lifter with mildly elevated creatinine and a normal eGFR is a common, usually benign pattern — bring both numbers to your clinician together.