Urine metabolomics for seronegative rheumatoid arthritis: an exploratory dual-platform analysis

Seronegative rheumatoid arthritis (negRA) is difficult to diagnose due to the absence of rheumatoid factor and anticitrullinated peptide antibodies. This observational case-control study analysed urine samples from 35 negRA patients and 25 healthy controls using integrated liquid chromatography-quadrupole time-of-flight mass spectrometry and gas chromatography-mass spectrometry. Data were processed using mass spectrometry-data independent analysis and evaluated with multivariate approaches, including orthogonal partial least squares discriminant analysis and receiver operating characteristic curve analysis. We identified distinct urinary metabolic alterations in negRA, with four metabolites showing moderate-to-excellent diagnostic accuracy (area under the curve: 0.78-0.91). Pathway analysis using the Kyoto Encyclopedia of Genes and Genomes indicated the involvement of redox regulation and nucleotide/cofactor metabolism. These findings support the potential of urine metabolomics as a non-invasive tool for biomarker discovery in negRA and warrant validation in larger cohorts.