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Fentanyl/Creatinine Ratio, Urine

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

A urine test that detects fentanyl and compares its amount with urine creatinine to help account for differences in urine concentration.

Quick summary

["This test can show whether fentanyl was present in a urine sample, but a result alone does not determine the dose or timing of exposure."]

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

Key facts at a glance

LOINC
58380-7
Short code
fentaNYL/Creat Ur
Synonyms
fentaNYL/Creat Ur
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?

This test measures fentanyl in urine and reports its amount relative to urine creatinine. Creatinine is used as a marker of urine concentration, so the ratio can help reduce the effect of variations in how concentrated or dilute a sample is.

Why might I need this test?

This test may be used in medication monitoring, substance-use assessment, workplace or school testing, or when a clinician needs to evaluate possible fentanyl exposure. It may also be part of a broader toxicology panel.

How is the test performed?

A urine sample is tested in the laboratory for fentanyl and creatinine. The laboratory calculates the fentanyl-to-creatinine ratio. If the initial result is unexpected or needs confirmation, the sample may also be evaluated with a more specific confirmatory method.

How do I prepare for the test?

Follow the collection instructions provided by the laboratory or clinician. Urine may need to be collected in a special cup at a specified time, and the sample should be returned promptly. Fasting is generally not required, but tell the clinician about all medications and substances you have used.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Urine Fentanyl/Creatinine Ratio

Frequently asked questions

Does a positive result mean someone was overdosed?
No. It shows that fentanyl was detected, but it does not by itself establish the dose, timing, or clinical severity of exposure.
Why is creatinine included?
Creatinine helps show how concentrated the urine is. Comparing fentanyl with creatinine reduces the effect of variations in urine concentration.
Can this test tell whether fentanyl was prescribed or illicit?
Not by itself. A clinician or testing professional must interpret the result along with the medical history, medication list, and other test findings.
  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