Test Catalog

Test ID: TRYPU    
Tryptophan, Random, Urine

Useful For Suggests clinical disorders or settings where the test may be helpful

Aiding in the screening and monitoring of Hartnup disease

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

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. Reduced intestinal absorption of tryptophan and subsequent loss in the urine lead to a reduction of available tryptophan for the synthesis of niacin. 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).

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

< or =35 months: 14-315 nmol/mg creatinine

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

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

> or =18 years: 18-114 nmol/mg creatinine

Interpretation Provides information to assist in interpretation of the test results

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.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Abnormal urine concentrations of tryptophan are not diagnostic for any particular disorder and must be interpreted in the context of a patient's clinical presentation and other laboratory results.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. 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

2. Levy HL: Hartnup Disorder. In The Online Metabolic and Molecular Bases of Inherited Disease. Edited by D Valle, AL Beaudet, B Vogelstein, et al. New York, McGraw-Hill, 2014. Accessed May 07, 2019 Available at http://ommbid.mhmedical.com/content.aspx?bookid=971&sectionid=62654267