PRTN3 and rheumatoid arthritis: To determine the diagnostic specificity and sensitivity sera from 290 RA patients (165 early and 125 established disease), 261 disease controls and 100 healthy subjects were tested for the presence of IgA, IgG, and IgM isotypes of RF, ACPA, and RA33 by EliATM platform (Phadia AB, Uppsala, Sweden).