Tryptophan/Creatinine Ratio, 24-Hour Urine
This test measures how much tryptophan is excreted in urine relative to creatinine over 24 hours. It can help evaluate altered tryptophan metabolism.
["The result reflects urinary tryptophan excretion relative to creatinine, which helps account for urine concentration."]
Key facts at a glance
- LOINC
- 25994-5
- Short code
- Tryptophan/Creat 24h Ur-sRto
- Synonyms
- Tryptophan/Creat 24h Ur-sRto
- Category
- kidney
- Sample
- urine
- Container
- Sterile urine container
- Units
- N/A
- Ref low
- 0.8
- Ref high
- 1.2
- Critical range
- 0.5 N/A – 5 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- CPT
- 85610
- SNOMED
- 396252006
- 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 is a 24-hour urine test that measures the amount of tryptophan, an essential amino acid, relative to creatinine, a waste product used as a marker of urine concentration. The ratio provides context when the amount or concentration of the urine collection varies.
Why might I need this test?
A clinician may order this test when symptoms suggest a problem with tryptophan metabolism or when evaluating an inherited condition that affects how the body processes amino acids. It may also be used alongside other nutritional, metabolic, and genetic tests.
How is the test performed?
You collect all urine produced during a full 24-hour period, usually beginning in the morning and ending the following morning. The laboratory measures tryptophan and creatinine in the collected urine and may calculate their ratio.
How do I prepare for the test?
Follow the collection instructions provided by your healthcare professional, including the start and end times and how the urine should be stored. Tell the clinician about major changes in your diet, medications, supplements, illness, or bowel and bladder habits because these can affect the result.
Reference range
INR: 0.8-1.2 (warfarin: 2.0-3.0)N/A
Inform your healthcare provider if you are taking blood thinners. No special preparation required.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
An abnormal result may reflect altered tryptophan metabolism, changes in kidney excretion, or differences in urine concentration. Reduced urinary tryptophan can occur in some inherited disorders of amino acid transport or metabolism, while elevated values may be associated with increased production, dietary or supplement effects, or certain other medical conditions. Results should be interpreted by a clinician together with symptoms, medications, diet, and other laboratory findings.
Short name
24-hour urine tryptophan/creatinine
Frequently asked questions
Why is creatinine included in this test?
How do I collect a 24-hour urine sample?
Do I need to change my diet before this test?
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 17, 2026. · Read our editorial policy