Serotonin-to-Creatinine Ratio, Urine
This urine test measures serotonin relative to creatinine, helping account for differences in urine concentration.
["The result can help evaluate serotonin production, particularly when symptoms suggest a serotonin-secreting condition."]
Key facts at a glance
- LOINC
- 34374-9
- Short code
- Serotonin/Creat Ur-sRto
- Synonyms
- Serotonin/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?
This test measures the amount of serotonin in urine relative to the amount of creatinine. Creatinine is used as a marker of urine concentration, so the ratio can make the serotonin result more meaningful than a urine serotonin measurement alone.
Why might I need this test?
A clinician may order this test when symptoms suggest excess serotonin activity, such as flushing, diarrhea, wheezing, or a rapid heartbeat. It may also be used to investigate suspected neuroendocrine tumors or monitor certain treatments.
How is the test performed?
A urine sample is collected and analyzed in the laboratory for serotonin and creatinine. The laboratory then compares the two measurements to calculate the reported ratio. Your clinician will tell you whether a single urine sample or a timed collection is required.
How do I prepare for the test?
Follow the collection instructions provided by the laboratory, including the time and amount of urine needed. Tell your clinician about medicines, supplements, and foods containing serotonin or tryptophan, because these may affect the result.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
An elevated urine serotonin-to-creatinine ratio may occur with a serotonin-secreting neuroendocrine tumor, including carcinoid syndrome, but it is not specific to these conditions. Food intake, medications, supplements, and temporary changes in urine concentration can also affect the result. An abnormal result should be interpreted by a clinician alongside symptoms and other testing.
Short name
Urine serotonin ratio
Frequently asked questions
What does the urine serotonin-to-creatinine ratio show?
What symptoms can lead to this test being ordered?
Do I need to collect urine for a specific period?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
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.
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