Neutrophil levels correlate with quantitative extent and progression of fibrosis in IPF: results of a single-centre cohort study

Background Idiopathic pulmonary fibrosis (IPF) is a progressive fibrotic lung disease with poor prognosis. Clinical studies have demonstrated association between different blood leukocytes and mortality and FVC decline. Here we question which blood leukocyte levels are specifically associated with progression of fibrosis, measured by accumulation of fibrosis on CT scan using a standardised automated method. Methods Using the CALIPER (Computer-Aided Lung Informatics for Pathology Evaluation and Rating) CT algorithm, we determined the correlation between different blood leukocytes (<4 months from CT) and total lung fibrosis (TLF) scores, pulmonary vessel volume (PVV), FVC% and TLCO% at baseline (n=171) and with progression of fibrosis (n=71), the latter using multivariate Cox regression. Results Neutrophils (but not monocyte or lymphocytes) correlated with extent of lung fibrosis (TLF/litre) (r=0.208, p=0.007), PVV (r=0.259, p=0.001), FVC% (r=-0.127, p=0.029) at baseline. For the 71 cases with repeat CT; median interval between CTs was 25.9 (16.8-39.9) months. Neutrophil but not monocyte levels are associated with increase in TLF/litre [HR 2.66, 95%CI, 1.35-5.25, p=0.005]. Conclusion Our study shows that neutrophil rather than monocyte levels correlated with quantifiable increase in fibrosis on imaging of the lungs in IPF, suggesting its relative greater contribution to progression of fibrosis in IPF. Key messages WHAT IS ALREADY KNOWN ON THIS TOPIC Idiopathic pulmonary fibrosis (IPF) is a progressive fibrotic condition. Recently, several human studies have implicated blood leukocyte levels (monocyte, neutrophil and lymphocyte) with FVC decline and mortality. However, direct association between leukocytes and progression of fibrosis using quantitative CT analysis has not been explored. WHAT THIS STUDY ADDS This study explored the association between blood monocytes, neutrophils and lymphocytes against increase in fibrosis over time, measured using a quantitative CT algorithm, CALIPER. We show that levels of blood neutrophil and lymphocytes but not monocytes were associated with greater risk of progression of fibrosis. HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE AND/OR POLICY Our study shows that neutrophil rather than monocyte levels correlated with quantifiable increase in fibrosis on imaging of the lungs in IPF, suggesting its relative greater contribution to progression of fibrosis in IPF.