The optimal cut-off value for MMP-7, MMP-9, MMP-10, and MMP-12 that achieved the best sensitivity and specificity were > 15,806 pg/mL, > 347,110 pg/mL, > 523.8 pg/mL and > 146.8 pg/mL, respectively, for the detection of ILD in RA patients (Additional File 2: Table S2), as well as > 21,564 pg/mL, > 302,893 pg/mL, > 382.1 pg/mL, > 203.7 pg/mL, respectively, for the identification of ILD in SSc patients (Additional File 2: Table S2). This evidence concerns the gene MMP9 and rheumatoid arthritis.