Creatinine
Muscle metabolism byproduct used as a kidney function marker
Also known as
Definition
Creatinine is a breakdown product of creatine phosphate metabolism and is excreted exclusively by the kidneys. It is the most common serum marker for estimating kidney function, though results are influenced by muscle mass and hydration status. The eGFR is preferred for more precise assessment; creatinine may be temporarily elevated with creatine supplementation.
| Parameter | Value |
|---|---|
| Unit | mg/dl (µmol/l) |
| Reference Range | Women: 0.50–0.90 mg/dl | Men: 0.70–1.20 mg/dl |
| Optimal Range (lab2go) | Women: 0.6–0.9 mg/dl | Men: 0.8–1.1 mg/dl |
Conversion: 1 mg/dl × 88.4 = µmol/l. US labs report creatinine in mg/dl; international literature also uses µmol/l.
↓ What a low value means
Low creatinine (< 0.5 mg/dl women, < 0.7 mg/dl men) occurs with reduced muscle mass (sarcopenia, cachexia, bed rest), malnutrition, vegetarian/vegan diet without creatine, or pregnancy (physiologically elevated GFR). A low value therefore does not necessarily indicate better kidney function — it often reflects less muscle mass.
↑ What a high value means
Creatinine above the reference range suggests impaired kidney function (eGFR decreases). Additional causes include dehydration (transient rise), high meat intake, intense physical exertion, and creatine supplementation (not a kidney injury). A rapid rise (> 0.3 mg/dl in 48 hours) requires urgent evaluation for acute kidney injury (obstruction, nephrotoxins, shock).
✓ How to optimize this marker
Stay well hydrated (1.5–2 L/day). Limit NSAID use to essentials. Control blood pressure and blood glucose. Creatine supplementation measurably raises creatinine without damaging the kidneys — inform your physician. If elevated: calculate eGFR; seek nephrology evaluation for persistent elevation.
When to test
No fasting required; avoid high-meat meals and intense exercise the day before (transient rise possible). Pause creatine supplements 48–72 hours prior for a representative kidney function estimate. Annual screening with hypertension, diabetes, or kidney disease risk.
Frequently asked questions
Does creatine supplementation damage the kidneys? +
No. In healthy kidneys at normal dosing (3–5 g/day), creatine supplementation is well documented as kidney-safe across numerous studies. The rise in serum creatinine is a laboratory artifact (more creatine → more creatinine in metabolism), not a sign of kidney damage.
Why is creatinine lower in women than in men? +
Women average less muscle mass than men, so less creatinine is produced and excreted. Reference ranges account for this difference. The eGFR calculation (CKD-EPI formula) also uses sex as a correction factor.
When should I see a nephrologist for elevated creatinine? +
Nephrology evaluation is indicated when creatinine is persistently above the reference range, rises rapidly (> 0.3 mg/dl in 48 hours), eGFR is < 60 ml/min/1.73 m² for more than 3 months, or when accompanied by proteinuria.
Sources
Last Reviewed: May 28, 2026 · sina
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.