Creatinine Test (Kidney Function)
Reviewed
Also called: Serum creatinine, Blood creatinine, Urine creatinine, Renal function
A creatinine test measures a muscle-related waste product used with other information to assess kidney filtration.
Specimen: Blood and/or urine
Why this test may be ordered
- Checking kidney health
- Diagnosing or monitoring kidney disease
- Monitoring medicines or conditions that can affect kidneys
Preparation and collection
The clinician or laboratory may advise avoiding cooked meat or fasting when creatinine is part of another panel. Do not stop medicines unless instructed.
Creatinine may be measured in a venous blood sample, a spot urine sample, or a timed urine collection. Follow the collection instructions exactly.
Blood collection has minor needle-related risks. Urine collection itself has no expected physical risk, but an incomplete timed collection can make the result unreliable.
Understanding results
Creatinine depends on kidney filtration but also muscle mass, diet, activity, hydration, age, pregnancy, and some medicines. Blood creatinine is commonly used to calculate eGFR.
- Higher blood creatinine: May indicate reduced kidney filtration, dehydration, obstruction, muscle injury, medicine effects, or other causes. Limitation: One value cannot diagnose a specific kidney condition or show whether a change is acute or chronic. Next step: Compare with prior results and assess eGFR, urine albumin, symptoms, medicines, and repeat testing.
- Within the printed interval: Falls within that laboratory's interval. Limitation: Early kidney disease may exist despite a creatinine result in range, especially when muscle mass is low. Next step: Interpret with eGFR, urine testing, risk factors, and trends.
- eGFR is an estimate and may be less reliable in unusual muscle mass or rapidly changing kidney function.
- Meat intake, supplements, intense exercise, hydration, and medicines can affect creatinine.
What to do next
Follow-up may include repeat creatinine/eGFR, urine albumin-to-creatinine ratio, electrolytes, imaging, or urgent assessment depending on the change and symptoms.
- Which reference interval and units apply to my result?
- Could medicines, supplements, illness, or sample timing affect this result?
- Do I need a repeat test or another test before any conclusion is made?
Evidence source
U.S. National Library of Medicine: Creatinine Test (Kidney Function)