Evaluation of the ratio of the average anti-major histocompatibility complex class I-related chain A (MICA) Ab levels to the average anti-human leukocyte antigen (HLA) class I Ab levels (MICA/Class I), as a marker for interstitial lung disease (ILD) in rheumatoid arthritis (RA) patients. (A) Distribution of the MICA/Class I ratio. Horizontal bars denote the means. The horizontal dotted line represents an optimized cut-off level (MICA/Class I = 0.770, with specificity and sensitivity of 0.882 and 0.824, respectively). ILD(+)RA: RA with ILD, ILD(−)RA: RA without ILD. (b) The receiver operating characteristic (ROC) curve using the MICA/Class I ratio (solid line) and KL-6 (dotted line) as markers for ILD in RA. The area under the curve (AUC) value of the ROC curve for MICA/Class I is 0.912 and that for KL-6 is 0.853. (C) Distribution of KL-6. Horizontal bars denote the means. The horizontal dotted line represents an optimized cut-off level (KL-6 = 296, with specificity and sensitivity of 0.824 and 0.875, respectively).