MUC1 and rheumatoid arthritis: ROC curve analysis to assess the diagnostic abilities of the three markers for the diagnosis of RA-ILD showed a superiority of KL-6 (Area under the curve, AUC: 0.79 95% CI 0.72–0.86, p<0.001) compared to SPD (AUC: 0.66 95% CI 0.58–0.74, p = 0.030) and CCL18 (AUC: 0.62, 95% CI 0.53–0.70, p = 0.007) (Fig 1D).