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Test ID: TRYPU Tryptophan, Urine

Reporting Name

Tryptophan, U

Useful For

Aids in the screening and monitoring of Hartnup disease

Specimen Type


Specimen Required

Container/Tube: Plastic, 10-mL urine tube (T068)

Specimen Volume: 2 mL

Collection Instructions: Collect a random urine specimen.

Additional Information:

1. Patient's age is required.

2. Include family history, clinical condition (asymptomatic or acute episode), diet, and drug therapy information.

Specimen Minimum Volume

1 mL

Specimen Stability Information

Specimen Type Temperature Time
Urine Frozen (preferred) 70 days
  Refrigerated  14 days

Reference Values

≤35 months: 14-315 nmol/mg creatinine

3-8 years: 10-303 nmol/mg creatinine

9-17 years: 15-229 nmol/mg creatinine

≥18 years: 18-114 nmol/mg creatinine

Day(s) and Time(s) Performed

Monday through Friday; 9 a.m. and 1 p.m.

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
TRYPU Tryptophan, U 28608-8


Result ID Test Result Name Result LOINC Value
83823 Tryptophan, U 28608-8
34618 Interpretation (TRYPU) 59462-2
113131 Reviewed By 18771-6

Clinical Information

Amino acids are the basic units that make up proteins and are crucial to virtually all metabolic processes in the body. Tryptophan is an essential amino acid necessary for the synthesis of serotonin, melatonin, and niacin.


Hartnup disease is a rare, usually benign, autosomal recessive disorder of renal and intestinal neutral amino acid transport. The clinical features associated with Hartnup disease include an erythematous skin rash on exposed surfaces that is identical to the rash seen in pellagra (niacin deficiency) and cerebral ataxia. Biochemically, it is characterized by increased renal excretion of tryptophan and other neutral amino acids. Newborn screening studies reveal that most affected individuals remain asymptomatic, suggesting that clinical expression of symptoms is dependent on additional genetic or environmental factors (ie, multifactorial disease).


Determination of tryptophan by conventional amino acid profiling methods (ninhydrin-based, HPLC) is hampered by coelution with other compounds. This liquid chromatography-tandem mass spectrometry method quantifies tryptophan and is interference free.


If the result is within the respective age-matched reference range, no interpretation is provided. When an abnormal result is reported, an interpretation may be added, including a correlation to available clinical information and recommendations for additional biochemical testing, if applicable.

Clinical Reference

Roth KS: Disorders of membrane transport. In Pediatric Endocrinology and Inborn Errors of Metabolism. Edited by K Sarafoglou, GF Hoffmann, KS Roth. New York, McGraw-Hill Medical Division, 2009, pp 108-112

Analytic Time

3 days (not reported on Saturday or Sunday)

Method Name

Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)


If not ordering electronically, complete, print, and send an Inborn Errors of Metabolism Test Request (T798) with the specimen. 

Mayo Clinic Laboratories | Genetics and Pharmacogenomics Catalog Additional Information: