Investigating inadequate tryptophan intake and monitoring dietary treatment
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.
Low plasma concentrations of tryptophan have been associated with clinical observations of insomnia, anxiety, and depression.
Glutaric acidemia type 1 is an autosomal recessive disorder of tryptophan and lysine metabolism caused by a deficiency of glutaryl-CoA dehydrogenase. Early diagnosis and treatment is essential to help prevent encephalopathic crises leading to brain degeneration. These can be provoked by infections, trauma, fever, and fasting. Treatment consists of preventing neurodegeneration through strict adherence to an emergency protocol. Dietary protein, in particular, lysine, is restricted during the vulnerable period of brain development from 0 to 5 years of age. In addition to other indices of malnutrition, the measurement of plasma concentration of tryptophan is used as an indicator of appropriate dietary therapy.
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 (LC-MS/MS) method quantifies tryptophan and is interference free.
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 =23 months: 17-75 nmol/mL
2 years-17 years: 23-80 nmol/mL
> or =18 years: 29-77 nmol/mL
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, elements of differential diagnosis, 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 plasma concentrations of tryptophan are not diagnostic for any particular disorder and must be interpreted in the context of a patient's clinical presentation.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Bremer HJ, Duran M, Kamerling JP, et al: In Disturbances of amino acid metabolism: Clinical Chemistry and Diagnosis. Edited by HJ Bremer, M Duran, JP Kamerling, et al. Baltimore-Munich, Urban and Schwarzenberg, 1981, pp 171-173
2. Hoffmann GF, Schulze A: Organic acidurias. 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