Tryptophan, Plasma
Use
This test is useful for investigating inadequate tryptophan intake and monitoring dietary treatment. 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. Conditions like glutaric acidemia type 1, a disorder of tryptophan and lysine metabolism, highlight the importance of early diagnosis and treatment to prevent encephalopathic crises and brain degeneration.
Special Instructions
Patient age is required along with family history, clinical condition (asymptomatic or acute episode), diet, and drug therapy information. Fasting for 4 hours is required; infants should have specimens collected before the next feeding. Body fluids are not acceptable specimens for this test. Use the Biochemical Genetics Test Request form if not ordering electronically.
Limitations
Abnormal plasma concentrations of tryptophan are not diagnostic for a specific disorder and must be interpreted in the context of the patient's clinical presentation and other laboratory results. Gross hemolysis, lipemia, or icterus are acceptable if they do not interfere with the analysis.
New York Approved
Methodology
Mass Spectrometry (LC-MS/MS)
Biomarkers
LOINC Codes
- 20659-9
- 20659-9
- 59462-2
- 18771-6
Result Turnaround Time
3-5 days
Related Documents
For more information, please review the documents below
Specimen
Plasma
Volume
0.5 mL
Minimum Volume
0.3 mL
Container
Plastic vial
Collection Instructions
Collect specimen into green top (sodium heparin) tube, place on wet ice, and centrifuge immediately or within 4 hours if refrigerated. Aliquot plasma into a plastic vial and freeze. Thrombin-activated tubes should not be used.
Patient Preparation
Fasting for 4 hours is required. Infants should have specimens collected before the next feeding (2-3 hours without total parenteral nutrition).
Stability Requirements
| Temperature | Period |
|---|---|
| Frozen | 14 days |