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 |
Agree on your personal target range with your doctor.
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 within a short time can point to acute kidney injury (obstruction, nephrotoxins, shock); in this case immediate medical evaluation is indicated.
✓ What can influence this value
Creatinine is influenced by muscle mass, hydration status, meat intake, and intense physical exertion. Creatine supplementation raises the measured value without any kidney damage being present. Dehydration can cause a temporary rise. Kidney function itself can be affected by conditions such as high blood pressure or diabetes and by medications that burden the kidneys (e.g., NSAIDs). The eGFR is additionally used for assessment; the assessment is made by the treating doctor.
When to test
Fasting is not needed. A high-meat meal or intense exercise the day before and creatine supplements can raise the value temporarily. Creatinine is measured, among other things, with high blood pressure, diabetes or a higher risk of kidney disease. Whether creatine is paused before the blood draw and how often the value is measured is decided by your doctor.
Frequently asked questions
Does creatine supplementation damage the kidneys? +
No. In healthy kidneys and in the amounts studied, 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 is elevated creatinine evaluated by a nephrologist? +
Whether a nephrology evaluation takes place is decided by your doctor. Factors include creatinine that stays above the reference range, a rapid rise, an eGFR that stays reduced for months, or accompanying proteinuria.
Creatinine
Sources
Last updated: May 28, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.