Souto-Carneiro1 M, Tóth L, Behnisch R, et al. - Researchers tried to find out whether differences in serum metabolites and lipids could aid in improving the differential diagnosis of these diseases. They obtained sera from seronegative rheumatoid arthritis (negRA) and psoriasis arthritis (PsA) individuals with established diagnoses to build a biomarker-discovery cohort and a blinded validation cohort. Samples were examined by proton nuclear magnetic resonance. This study estimated metabolite concentrations from the spectra and used to select the variables to build a multivariate diagnostic model. The study demonstrated that PsA and negRA have distinct serum metabolomic and lipidomic signatures that can be applied as biomarkers to discriminate between them. This diagnostic model may become an important tool for a definite diagnosis of negRA or PsA individuals after validation in larger multiethnic cohorts.