Subgroup analysis by age showed significant differences in CRP concentrations between RA-ILD and RA groups among older adults (aged ≥60 years) (MD = 6.39; 95% CI: 3.19-9.59; P < 0.001), but not among younger individuals (aged <60 years) (MD = 16.94; 95% CI: -0.72-34.60; P = 0.06) (Table 2). This evidence concerns the gene CRP and rheumatoid arthritis.