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Creatinine, Blood/Serum and Urine

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

Measures creatinine in blood and urine. When reported together, the levels may be used to calculate a urine-to-serum creatinine ratio and help assess kidney function.

Quick summary

["Creatinine measurements help clinicians evaluate kidney filtration, hydration, and muscle metabolism."]

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

Key facts at a glance

LOINC
79619-3
Short code
S-B-AIB/Creat Ur-sRto
Synonyms
S-B-AIB/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?

Creatinine is a waste product produced by the muscles and filtered by the kidneys. This test measures its concentration in blood or serum and urine; the results may also be used to calculate the amount of creatinine being cleared by the kidneys.

Why might I need this test?

A clinician may order these measurements to evaluate kidney function, investigate changes in urination, monitor illness or medication use, or assess the effects of dehydration. A urine-to-serum creatinine ratio can provide additional information when interpreted with other findings.

How is the test performed?

A blood sample and a urine sample are analyzed for creatinine. Depending on the test, urine may be collected once or over a specified period, and the laboratory may calculate a urine-to-serum creatinine ratio.

How do I prepare for the test?

Fasting is generally not required. Follow the instructions provided for urine collection, including whether a timed collection is needed, and tell your clinician if you have recently had unusually heavy fluid loss or changes in muscle mass.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Blood and urine creatinine

Frequently asked questions

Why are creatinine measured in both blood and urine?
The two measurements show how much creatinine is in the blood compared with the amount being excreted in urine. This can help clinicians evaluate kidney filtration and identify changes in hydration or muscle mass.
Do I need to fast for this test?
Fasting is usually not necessary. Follow the laboratory's instructions for urine collection, especially if a timed urine specimen is requested.
What can cause an abnormal creatinine result?
Kidney impairment, dehydration, medications, urinary obstruction, and changes in muscle mass can affect the results. Your clinician will interpret an abnormal value using your symptoms, medical history, and other laboratory tests.
  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