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Serum Creatinine (with optional 24-hour urine collection for creatinine clearance calculation)

Published: August 9, 2026Updated: August 16, 2026

This test measures the amount of creatinine, a waste product from muscle breakdown, in your blood or urine to help assess kidney function.

Quick summary

["Kidney health and function depend on this simple blood or urine test."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
36031-3
Short code
MR SIJ
Synonyms
MR SIJ
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
mr
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why Your Kidneys Matter

Kidneys filter waste and extra fluids from your blood. Creatinine is a byproduct of muscle metabolism that builds up when kidneys aren’t working well. High levels may signal kidney problems.

What This Test Shows

A blood test checks creatinine levels in serum. If your doctor orders a 24-hour urine test, they’ll measure creatinine in your urine over 24 hours to calculate how well your kidneys filter waste.

When You Might Need This Test

Doctors may check creatinine levels if you have symptoms like swelling, fatigue, or frequent urination. It’s also part of routine health checks, especially for people with diabetes, high blood pressure, or a family history of kidney disease.

What to Expect Before the Test

No special preparation is needed for a blood test. For urine tests, collect all urine for 24 hours in a special container. Drink enough water to produce clear urine, but avoid excessive fluids that could dilute results.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Creatinine

Frequently asked questions

How high or low your creatinine levels might indicate kidney problems or other health conditions, such as dehydration or muscle disorders.
Creatinine levels alone don’t diagnose kidney disease. Doctors compare them with other tests, like blood pressure or protein in urine, to assess kidney function fully.
FAQ: What causes creatinine levels to change?
Changes can occur due to muscle mass (more muscle = higher levels), dehydration, kidney disease, or certain medications. Dietary protein intake may also affect results, but it’s usually less impactful than kidney function.
FAQ: Can I eat or drink before a blood test?
Yes, eat your usual meals and drink water unless instructed otherwise. Avoid alcohol or large amounts of caffeine before testing, as they may temporarily affect results.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy