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Urine-to-Serum Creatinine Ratio

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

A calculated test comparing the amount of creatinine in urine with the amount in blood, often used to assess kidney function and urine concentration.

Quick summary

["This ratio compares urine and blood creatinine and must be interpreted with hydration, urine output, and other clinical findings."]

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

Key facts at a glance

LOINC
77184-0
Short code
Nb/Creat Ur-sRto
Synonyms
Nb/Creat Ur-sRto
Category
kidney
Sample
urine
Container
Sterile urine container
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Specimen volume
10 mL
Stability
Room temperature: 2h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

What is this test?

The urine-to-serum creatinine ratio compares the concentration of creatinine in a urine sample with its concentration in a blood sample. Creatinine is a waste product made by the muscles and filtered by the kidneys.

Why might I need this test?

This test may be used to evaluate how the kidneys concentrate urine and handle creatinine. It can provide information in the evaluation of reduced urine output, suspected kidney injury, and certain kidney conditions.

How is the test performed?

A urine sample and a blood sample are collected, usually close together in time. The laboratory divides the urine creatinine result by the serum creatinine result to calculate the ratio.

How do I prepare for the test?

Follow the collection instructions provided by your healthcare professional, and tell the laboratory if you are dehydrated or have recently had intense exercise. If a 24-hour urine collection is requested, collect all urine for the full period and include it at the specified time.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Urine/serum creatinine ratio

Frequently asked questions

Is fasting required for this test?
Fasting is usually not required, but follow your clinician's instructions. Heavy exercise and a large high-protein or high-meat meal can temporarily affect creatinine, so mention recent activity and diet when the sample is collected.
Why are both a urine sample and a blood sample needed?
The urine creatinine value alone does not show how concentrated the urine is. Comparing it with the blood creatinine value provides context about kidney function and urine production.
Can this ratio diagnose a kidney disease?
No. An abnormal ratio can suggest several processes, including dehydration or impaired kidney function, and must be interpreted with the rest of your clinical evaluation.
  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