What Is Creatinine in a Blood Test?
Creatinine is a waste product from muscle metabolism. Your kidneys filter it constantly, making it a reliable marker of kidney function.
Normal Range
- Men: 0.7–1.3 mg/dL
- Women: 0.6–1.1 mg/dL
High Creatinine Causes
- Chronic kidney disease — progressive loss of filtering capacity
- Acute kidney injury — sudden drop from dehydration, medications, infection
- High muscle mass — bodybuilders may have naturally higher creatinine
- High meat intake
- Rhabdomyolysis — massive muscle breakdown
- Medications — NSAIDs, ACE inhibitors
Low Creatinine Causes
- Low muscle mass — elderly, cachectic patients
- Pregnancy — increased GFR dilutes
- Liver disease
- Malnutrition
Creatinine and eGFR
- eGFR is calculated from creatinine + age + sex
- A muscular young man with creatinine 1.2 may have normal kidneys
- A frail elderly woman with creatinine 1.0 may have reduced function
- Always interpret with eGFR, not creatinine alone
Source: NLM MedlinePlus, American Association for Clinical Chemistry.
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