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 >= 0.6x10(9) and >0.9x10(9) cells<middle dot>L-1 for unadjusted models and >= 0.95x10(9) cells<middle dot>L-1 for adjusted models, using random effects, with heterogeneity and bias assessed. Disease progression associated with monocytes >0.9x10(9)cells<middle dot>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 >= 0.6x10(9) cells<middle dot>L-1 was 1.71 (95% CI 1.34-2.19, p<0.001, I-2=0%) and for monocyte counts >0.90x10(9) cells<middle dot>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 >= 0.95x10(9) cells<middle dot>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.