Identification of prognostic and predictive biomarkers in idiopathic pulmonary fibrosis (IPF) could aid assessment of disease severity and prediction of progression and response to treatment. This analysis examined reference ranges for neutrophil-lymphocyte ratio (NLR) and platelet-lymphocyte ratio (PLR) in IPF, and the relationship between NLR or PLR changes and clinical outcomes over 12 months. This post hoc analysis included patients with IPF from the Phase III, double-blind trials of pirfenidone, ASCEND (NCT01366209) and CAPACITY (NCT00287716 and NCT00287729). The relationship between change from baseline to Month 12 in NLR or PLR (divided into quartiles (Q1-Q4)) and outcomes (mortality, respiratory hospitalization, declines in lung function, exercise capacity and quality of life) was assessed. Estimated reference ranges at baseline for all patients analyzed ( = 1334) were 1.1-6.4 for NLR and 56.8-250.5 for PLR. Significant trends were observed across NLR and PLR quartiles for all outcomes in placebo-treated patients, with patients manifesting the greatest NLR or PLR changes experiencing the worst outcomes. These results suggest that the greatest NLR or PLR changes over 12 months were associated with worse clinical outcomes. Further research is needed to determine the utility of NLR and PLR as prognostic biomarkers in IPF.