Indicator Explainer
Cysteine
A non-essential sulfur-containing amino acid in humans, related to cystine, Cysteine is important for protein synthesis, detoxification, and diverse metabolic functions. Found in beta-keratin, the main protein in nails, skin, and hair, Cysteine is important in collagen production, as well as skin elasticity and texture. Also required in the manufacture of amino acid taurine, Cysteine is a component of the antioxidant glutathione, and plays a role in the metabolism of essential biochemicals such as coenzyme A, heparin, and biotin. (NCI04)
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, C29609. 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 — Cysteine (C29609)
- Source: National Cancer Institute, NCI Thesaurus 26.09d, C29609. NCI definition, reproduced without modification under CC BY 4.0.
- A Fluorogenic Cysteine-Tetrapeptide Tagging Strategy for Nonperturbative Protein Labeling and Protein-Ligand Interaction Tracking. — Adv Sci (Weinh), 2026-10-15 (PMID 42885169; literature)
- A Red-Emissive TCF-Based Fluorescent Probe for Selective Cysteine Detection in Food Samples and Living Cells. — J Fluoresc, 2026-10-24 (PMID 42925356; literature)
- Nodule Cysteine-Rich (NCR) Peptides as Next-Generation Antimicrobials: A Computational Perspective on Structure, Mechanism, and Drug Design. — Probiotics Antimicrob Proteins, 2026-10-23 (PMID 42909843; literature)
- The taste of cysteine cathepsins: analyzing specificity, aiming for function. — Biol Chem, 2026-10-26 (PMID 42926324; literature)
- Inhibition Kinetics of Protein Inhibitors of Carboxypeptidase-A and Cysteine Protease Isolated from Non-Host Plants of Helicoverpa armigera Against Gut Proteases. — Protein J, 2026-10-25 (PMID 42927596; literature)