Indicator Explainer
Cystine
Not considered one of the 20 amino acids, Cystine is a sulfur-containing derivative obtained from oxidation of cysteine amino acid thiol side chains. It functions as an antioxidant and protects tissues against radiation and pollution, slowing the aging process. It also aids protein synthesis. Cystine is abundant in many proteins of skeletal tissues and skin, and found in insulin and digestive enzymes chromotrypsinogen A, papain, and trypsinogen. (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, C29610. 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
References
- NCI Thesaurus 26.09d — Cystine (C29610)
- Source: National Cancer Institute, NCI Thesaurus 26.09d, C29610. NCI definition, reproduced without modification under CC BY 4.0.
- PCSK9 drives acquired resistance to anti-PD-1 immunotherapy through cystine metabolic reprogramming in lung cancer. — J Immunother Cancer, 2026-10-20 (PMID 42901717; literature)
- Cystine as an Ionophore: Redox-Controlled Anion Transport and Toxicity Toward Triple Negative Breast Cancer Cells. — Chemistry, 2026-10-14 (PMID 42876151; literature)
- NRF2 coordinates cystine import and glutathione use to sustain ferroptosis resistance and formaldehyde tolerance in cancer. — Sci Adv, 2026-10-23 (PMID 42913006; literature)
- Astrocytic Cystine/Glutamate Antiporters Promote Diabetic Encephalopathy via the Induction of Glutamate Excitotoxicity. — Diabetes Metab J, 2026-10-21 (PMID 42906899; literature)