Interstitial lung disease (ILD) is a common pulmonary manifestation of rheumatoid arthritis (RA) associated with clinical heterogeneity and high mortality. This study aimed to determine whether non-invasive biomarkers, especially monocyte count in peripheral blood, would be useful for predicting outcomes in patients with RA-associated ILD (RA-ILD).

We retrospectively reviewed the medical records of 72 patients with RA-ILD. We assessed clinical characteristics, laboratory findings at the time of diagnosis. We used Cox proportional hazard analyses to determine significant variables associated with outcomes. Cumulative survival rates were calculated using the Kaplan–Meier method.

The median age was 68.6 years (58% male). The 5-year survival rate was 78.4%. Cox proportional hazard analyses adjusted by age and sex showed that increased monocyte count and neutrophil count were significantly associated with poor prognosis in patients with RA-ILD. According to optimal cutoff levels, patients with high monocyte counts (≥458/μl) had significantly lower survival rates than those with low monocyte counts (<458/μl). Similarly, patients with high neutrophil counts (≥9394/μl) had significantly lower survival rates than those with low neutrophil counts (<9394/μl). Combinatorial assessments with peripheral monocyte and neutrophil counts revealed that the patients with both high monocyte and neutrophil counts had the lowest survival.

Increased monocyte and neutrophil counts might be potential cellular biomarkers to predict poor outcomes in patients with RA-ILD.