Creatinine
A waste product from muscle metabolism that your kidneys filter out. Used to assess kidney function.
What is Creatinine?
Creatinine is a waste product produced when your muscles break down creatine, a compound used for energy during muscle contractions. Your body produces creatinine at a relatively constant rate.
Healthy kidneys filter creatinine out of the blood and excrete it in urine. When kidney function declines, creatinine builds up in the bloodstream.
This makes creatinine a useful marker for kidney health — not because it's harmful itself, but because elevated levels indicate your kidneys aren't filtering efficiently.
Normal Ranges
| Group | Creatinine Level |
|---|---|
| Adult men | 0.7–1.3 mg/dL (62–115 µmol/L) |
| Adult women | 0.6–1.1 mg/dL (53–97 µmol/L) |
Normal ranges vary by laboratory. Muscular individuals may have naturally higher creatinine levels without kidney problems.
Why It Matters
Kidney Function Assessment
Creatinine is used to calculate eGFR, the primary measure of kidney function. Rising creatinine often signals declining kidney health.
Medication Monitoring
Many medications affect or are affected by kidney function. Doctors check creatinine before prescribing certain drugs and monitor it during treatment.
Dehydration Detection
Temporary spikes in creatinine can indicate dehydration, which reduces blood flow to the kidneys.
What Affects Creatinine
Several factors influence creatinine levels:
- Muscle mass — More muscle means more creatinine production
- Diet — High meat consumption can temporarily raise levels
- Supplements — Creatine supplements increase creatinine
- Intense exercise — May cause temporary elevation
- Hydration — Dehydration concentrates creatinine in blood
Creatinine vs. eGFR
Creatinine alone doesn't tell the whole story. A muscular 25-year-old and an 80-year-old might have the same creatinine, but very different kidney function.
That's why eGFR exists — it adjusts creatinine for age, sex, and body size to give a more accurate picture.
How Often to Test
- Routine checkups: Typically included in standard blood panels
- Chronic conditions: Annually or more frequently
- Taking kidney-affecting medications: As directed
Related Biomarkers
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