Creatinine

Metabolic Panel

What is Creatinine?

Creatinine is a waste product generated from the normal breakdown of creatine phosphate in skeletal muscles during energy metabolism. Your muscles use creatine phosphate as a quick energy source, and as it is metabolized, creatinine is produced at a relatively constant rate determined by your muscle mass. Creatinine enters the bloodstream and is filtered out almost entirely by the kidneys, making it an excellent marker of kidney filtration function.

The serum creatinine test measures the concentration of creatinine in your blood. Because creatinine production is relatively stable and its excretion depends almost entirely on kidney function, rising creatinine levels indicate declining kidney function. Creatinine is used to calculate the estimated glomerular filtration rate (eGFR), which is the gold standard for assessing kidney function and staging chronic kidney disease. However, creatinine levels must be interpreted in context—muscle mass, age, sex, race, diet, and hydration status all influence baseline creatinine levels.

Why It Matters

Creatinine is one of the most important markers of kidney health. The kidneys filter roughly 180 liters of blood daily, and even modest declines in kidney function can lead to creatinine accumulation. Elevated creatinine may indicate acute kidney injury, chronic kidney disease, or obstruction of the urinary tract. Since kidney disease is often silent in early stages, creatinine monitoring can detect problems before symptoms appear. It is also essential for adjusting medication doses, as many drugs are cleared by the kidneys.

Normal Reference Ranges

Group	Range	Unit
Adult Men	0.74–1.35	mg/dL
Adult Women	0.59–1.04	mg/dL
Children (3–18 years)	0.3–0.7	mg/dL
eGFR (Normal)	90–120	mL/min/1.73m²

Reference ranges may vary by laboratory. Always compare results to the ranges provided by your testing facility.

What High Cr Levels Mean

Common Causes

Chronic kidney disease
Acute kidney injury (dehydration, sepsis, medications)
Urinary tract obstruction (kidney stones, enlarged prostate)
High muscle mass or excessive creatine supplementation
High-protein diet (temporary increase)
Medications (ACE inhibitors, NSAIDs, certain antibiotics)
Rhabdomyolysis (muscle breakdown)

Possible Symptoms

Often asymptomatic in early kidney disease
Swelling in legs, ankles, or feet
Decreased urine output
Fatigue and weakness
Nausea and loss of appetite
Shortness of breath
Confusion (in severe cases)

What to do: Elevated creatinine warrants investigation of kidney function with eGFR calculation, urinalysis, kidney ultrasound, and review of medications. Identify and treat reversible causes such as dehydration, urinary obstruction, or nephrotoxic drugs. For chronic kidney disease, management includes blood pressure control, diabetes management, dietary protein and sodium restriction, and avoidance of nephrotoxic agents. Referral to a nephrologist is recommended for eGFR below 30 mL/min.

What Low Cr Levels Mean

Common Causes

Low muscle mass (elderly, malnourished, or debilitated patients)
Severe liver disease (reduced creatine production)
Pregnancy (increased kidney filtration)
Excessive hydration
Muscle-wasting diseases (muscular dystrophy)

Possible Symptoms

Low creatinine itself rarely causes symptoms
Symptoms relate to underlying conditions: muscle weakness, weight loss, fatigue

What to do: Low creatinine is less common as a clinical concern but may indicate reduced muscle mass or liver disease. Evaluation should focus on the underlying cause—nutritional assessment, liver function tests, and evaluation of muscle disorders. In elderly or debilitated patients, a low creatinine can mask kidney disease because less creatinine is produced; cystatin C-based eGFR may provide a more accurate assessment of kidney function in these cases.

When Is Cr Testing Recommended?

Annual screening, especially for those with diabetes or hypertension
When taking medications that affect the kidneys
When experiencing symptoms of kidney dysfunction
Before procedures involving contrast dye
To monitor known chronic kidney disease
During hospitalization for acute illness

Frequently Asked Questions

Estimated glomerular filtration rate (eGFR) is a calculation that estimates how many milliliters of blood your kidneys filter per minute. It is calculated from serum creatinine using the CKD-EPI equation, which factors in age and sex (the 2021 equation no longer includes a race variable). An eGFR above 90 mL/min is normal, 60–89 is mildly decreased, 30–59 is moderately decreased, 15–29 is severely decreased, and below 15 indicates kidney failure. eGFR is more useful than creatinine alone because it accounts for individual variation in creatinine production.

Yes. Eating a large amount of cooked meat can temporarily raise creatinine because cooking converts creatine in meat to creatinine, which is absorbed and enters the blood. Creatine supplements, popular among athletes, are metabolized to creatinine and can increase serum levels by 0.1–0.3 mg/dL without actual kidney damage. A vegetarian diet may result in lower creatinine due to reduced dietary creatine intake. For the most accurate results, maintain your usual diet before testing and inform your doctor about any supplements.

Creatinine is produced by muscles, so levels correlate with muscle mass. On average, men have greater muscle mass than women, resulting in higher creatinine production and higher normal ranges. This is why the same creatinine level may indicate different kidney function in a man versus a woman—the eGFR calculation adjusts for sex to account for this difference. Similarly, bodybuilders may have higher creatinine than sedentary individuals of the same sex without any kidney problem.

Related Biomarkers

BUNBlood Urea Nitrogen GLUGlucose KPotassium NaSodium CaCalcium

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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Reference ranges may vary between laboratories. Always consult your healthcare provider for interpretation of your specific test results.