Creatinine: Blood Levels, Kidney Function, and Clinical Significance

What Is Creatinine?

Creatinine is a waste product generated from the breakdown of creatine phosphate in muscle tissue. It is filtered by the kidneys and excreted in urine. The name derives from Greek kreas (flesh/meat).

Normal Ranges (approximate)

• Adult males: 0.7–1.3 mg/dL
• Adult females: 0.6–1.1 mg/dL

Factors Affecting Levels

• Muscle mass: Higher muscle mass → higher creatinine.
• Diet: High meat intake transiently raises levels.
• Kidney function: Impaired glomerular filtration rate (GFR) increases serum creatinine.
• Medications: Some drugs (e.g., trimethoprim, cimetidine) interfere with secretion.

Clinical Use

Serum creatinine is a key marker for estimating GFR and assessing kidney health. Trends over time are more informative than a single value.