Creatinine
Creatinine· also: Creatinine, Serum Creatinine
Clinical Overview
Creatinine is a waste product from normal muscle metabolism, produced at a steady rate and excreted almost entirely by the kidneys. Because its production is relatively constant, creatinine is an excellent marker of kidney filtration function. It is always interpreted alongside eGFR and compared to the patient's baseline.
Why This Test Matters
Creatinine is the most widely used test to detect and monitor kidney disease. A doubling of creatinine represents approximately a 50% loss of kidney function. Creatinine rises in acute kidney injury (AKI) and chronic kidney disease (CKD). However, creatinine can remain within the normal range even when up to 50% of kidney function is lost — eGFR is more sensitive for early CKD.
Reference RangesWHO/IFCC standards
| Age Group | Sex | Reference Range | Unit | Notes |
|---|---|---|---|---|
| Adults (18–64) | Male | 0.7 – 1.3 | mg/dL | — |
| Adults (18–64) | Female | 0.5 – 1.1 | mg/dL | — |
Also reported in: µmol/L.Conversion factor: 1 µmol/L = 88.496 mg/dL.
Critical (Panic) Values
Critical High: > 10 mg/dL. Values outside these limits require immediate clinical attention.
What Causes Abnormal Results?
High Creatinine Causes
- Acute kidney injury (AKI): dehydration, sepsis, medications (NSAIDs, contrast dye)
- Chronic kidney disease (CKD): diabetes, hypertension, glomerulonephritis
- Rhabdomyolysis (muscle breakdown releasing creatinine and myoglobin)
- Urinary tract obstruction
- High dietary meat intake (transient mild rise)
- Creatine supplements
Low Creatinine Causes
- Low muscle mass (elderly, malnutrition, muscle-wasting diseases)
- Pregnancy (increased GFR and plasma volume dilute creatinine)
- Liver disease (reduced creatine synthesis)
Signs & Symptoms to Watch For
How to Prepare for This Test
Avoid heavy meat consumption the day before testing, as this can transiently raise creatinine. Avoid creatine supplements for at least 24 hours. Inform your doctor of all medications.
Factors That Can Affect Results
- High meat intake (raises creatinine transiently)
- Creatine supplements (significantly raise creatinine)
- Cimetidine and trimethoprim (block tubular secretion of creatinine, raising measured level without true GFR change)
- Low muscle mass (gives falsely low creatinine, masking kidney disease)
- Hemolysis, jaundice, lipemia (can interfere with older colorimetric assays)
Related Topics
Frequently Asked Questions
What creatinine level indicates kidney failure?
There is no single creatinine level that defines kidney failure — it must be interpreted in context. A creatinine of 2 mg/dL may represent end-stage kidney disease in a small elderly woman with low muscle mass, while the same value in a large muscular man may reflect much better kidney function. The eGFR, calculated from creatinine adjusted for age, sex, and race, is a more accurate measure of kidney function.
How fast does creatinine rise in acute kidney injury?
In acute kidney injury, creatinine typically rises by 0.3 mg/dL or more within 48 hours, or by 50% or more from baseline within 7 days (KDIGO AKI definition). The rate of rise reflects the severity of the insult and the remaining kidney reserve. In patients who develop AKI requiring dialysis, creatinine can rise by 1–2 mg/dL per day if no kidney function remains.