Indicator Explainer
Citrulline
A non-essential amino acid. In hepatocytes, L-citrulline is synthesized in the urea cycle by the addition of carbon dioxide and ammonia to ornithine. L-citrulline is converted into L-arginine by the enzymes argininosuccinate synthetase and argininosuccinate lyase in the presence of L-aspartate and ATP. Subsequently, L-arginine is converted to nitric oxide by nitric oxide synthase and L-citrulline is regenerated as a by-product.
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, C53406. 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.