ISM1 and rheumatoid arthritis: Healthy controls exhibited markedly higher serum ISM1 levels (median (IQR), 678 (710) ng/L) than both early RA patients (≤12 weeks) (347 (142) ng/L; p < 0.001) and established RA patients (>12 weeks) (341 (256) ng/L; p < 0.001).