Tryptophan-to-Creatinine Ratio, Urine
A urine test that compares the amount of tryptophan with the amount of creatinine, which can help assess tryptophan metabolism and excretion.
["This ratio may help evaluate how your body handles and eliminates tryptophan, but results must be interpreted with diet and other clinical findings."]
Key facts at a glance
- LOINC
- 28608-8
- Short code
- Tryptophan/Creat Ur-Rto
- Synonyms
- Tryptophan/Creat Ur-Rto
- 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 test measures tryptophan and creatinine in a urine sample. Creatinine is a waste product used as an internal comparison, and the ratio can help show how much tryptophan is being excreted relative to urine concentration.
Why might I need this test?
A clinician may order this test when evaluating how the body absorbs, transports, or metabolizes tryptophan, an essential amino acid. It may be part of an assessment of nutritional, metabolic, or kidney-related symptoms.
How is the test performed?
The laboratory measures the amount of tryptophan and creatinine in the urine provided. The results are calculated as a ratio. The type of urine collection, such as a single sample or a timed collection, depends on the instructions from your clinician.
How do I prepare for the test?
Follow the urine-collection instructions provided by the healthcare professional. Record the collection time and total urine volume if this is a timed collection, and tell the laboratory if you recently changed your diet, took supplements, or started new medicines.
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 ratio may reflect differences in tryptophan intake, vitamin availability, metabolism, kidney handling, or urine concentration. These findings are not specific to one condition and should be interpreted alongside symptoms, diet, medicines, and other laboratory tests by a qualified clinician.
Short name
Urine tryptophan/creatinine ratio
Frequently asked questions
Does this test require a fasting blood sample?
Why is creatinine included in the result?
Can this test diagnose a condition by itself?
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