Indicator Explainer
L-Tyrosine
The levorotatory isomer of the aromatic amino acid tyrosine. L-tyrosine is a naturally occurring tyrosine and is synthesized in vivo from L-phenylalanine. It is considered a non-essential amino acid; however, in patients with phenylketonuria who lack phenylalanine hydroxylase and cannot convert phenylalanine into tyrosine, it is considered an essential nutrient. In vivo, tyrosine plays a role in protein synthesis and serves as a precursor for the synthesis of catecholamines, thyroxine, and melanin.
This page explains what the indicator is and how results are interpreted in general terms. Reference ranges depend on the laboratory, the method, and your own situation — no single “normal value” applies to everyone. This page is health information, not a diagnosis. For symptoms, treatment, or urgent concerns, contact a healthcare professional.
When it is tested
Source: National Cancer Institute, NCI Thesaurus 26.09d, C915. NCI definition, reproduced without modification under CC BY 4.0. Source identity and definition checked automatically on 2026-10-20. No individual clinical interpretation or human reviewer is asserted.
Reading results
Reference intervals and interpretation depend on the laboratory, specimen, method and clinical context. This source definition is educational information; it does not establish a diagnosis, product approval or suitability for an individual.
Also Known As
Related Tests
Tests that measure or involve this indicator.
References
- NCI Thesaurus 26.09d — L-Tyrosine (C915)
- Source: National Cancer Institute, NCI Thesaurus 26.09d, C915. NCI definition, reproduced without modification under CC BY 4.0.
- From human allergen immunotherapy to veterinary prophylactic vaccines: translational potential of Microcrystalline tyrosine as a vaccine adjuvant. — Vet Res Commun, 2026-09-29 (PMID 42809146; literature)
- Exploring L-tyrosine and L-DOPA biosynthesis in faba bean (Vicia faba L.). — Ann Bot, 2026-09-21 (PMID 42765826; literature)
- Multienzyme cascade biotransformation of L-Tyrosine to Danshensu by engineered Escherichia coli. — PLoS One, 2026-10-23 (PMID 42912794; literature)
- Nitrogen- and Sulfur-Co-Doped Reduced Graphene Oxide-Based Antifouling Electrochemical Sensor for the Detection of l-Tyrosine. — Langmuir, 2026-09-01 (PMID 42916812; literature)