Prognostic Significance of Peripheral Blood Monocyte Count Among a National Cohort of Veterans with Pulmonary Fibrosis.

Introduction: Elevated peripheral blood monocyte counts (PBMC) are associated with disease progression and mortality in patients with idiopathic pulmonary fibrosis (IPF). However, evidence for progression stems primarily from highly curated cohort studies or post-hoc analysis of clinical trials. We used real-world data to examine the association between PBMC and IPF mortality among a national cohort of Veterans with IPF.

Methods: We used an ICD-code based electronic health record algorithm to identify Veterans with IPF. Those who had PBMC available within 180 days of index IPF diagnosis were included in the analytical cohort. Mortality analyses were conducted using Cox proportional hazard models.

Results: We identified 30,419 Veterans with IPF and a PBMC available for analysis. Veterans with PBMC ≥ 0.95 x 109 cells/L had a 51% higher risk of all-cause mortality (HR 1.51, 95% CI 1.44 - 1.58, p<0.001) in an unadjusted analysis. The risk persisted in models adjusted for age and sex (HR 1.43, 95% CI 1.36 - 1.50, p<0.001) and after adjustment for oxygen utilization as a surrogate marker of disease severity (HR 1.35, 95% CI 1.29 - 1.41, p<0.001). There was a stepwise increase in mortality risk as peripheral blood monocyte counts increased with a monocyte dichotomization threshold between 0.4 and 0.5 x 109 cells/L associated with HR for mortality of greater than 1.0 for both unadjusted and adjusted models.

Conclusion: We found that a stepwise increase in PBMC was associated with an increased all-cause IPF mortality. A PBMC dichotomization threshold between 0.4 and 0.5 x 109 cells/L, which is lower than previously reported, was associated with an increased risk of mortality.