Peripheral blood monocyte count and outcomes in patients with interstitial lung disease: a systematic review and meta-analysis

Background Peripheral blood monocyte counts have been associated with poor outcomes in interstitial lung disease (ILD). However, studies are limited by variable biomarker thresholds, analytic approaches and heterogenous populations. This systematic review and meta-analysis characterised the relationship between monocytes and clinical outcomes in ILD. Methods Electronic database searches were performed. Two reviewers screened abstracts and extracted data. Pooled estimates (hazard ratios (HRs)) of monocyte count thresholds were calculated for their association with mortality using ≥0.6×10 9 and >0.9×10 9 cells·L −1 for unadjusted models and ≥0.95×10 9 cells·L −1 for adjusted models, using random effects, with heterogeneity and bias assessed. Disease progression associated with monocytes >0.9×10 9 cells·L −1 was also calculated. Results Of 3279 abstracts, 13 were included in the systematic review and eight in the meta-analysis. The pooled unadjusted HR for mortality for monocyte counts ≥0.6×10 9 cells·L −1 was 1.71 (95% CI 1.34–2.19, p<0.001, I 2 =0%) and for monocyte counts >0.90×10 9 cells·L −1 it was 2.44 (95% CI 1.53–3.87, p=0.0002, I 2 =52%). The pooled adjusted HR for mortality for monocyte counts ≥0.95×10 9 cells·L −1 was 1.93 (95% CI 1.24–3.01, p=0.0038 I 2 =69%). The pooled HR for disease progression associated with increased monocyte counts was 1.83 (95% CI 1.40–2.39, p<0.0001, I 2 =28%). Conclusions Peripheral blood monocyte counts were associated with an increased risk of mortality and disease progression in patients with ILD.