Serum C‐reactive protein is associated with earlier mortality across different interstitial lung diseases

Abstract Background and Objective The acute‐phase protein C‐reactive protein (CRP) is known to be associated with poor outcomes in cancer and cardiovascular disease, but there is limited evidence of its prognostic implications in interstitial lung diseases (ILDs). We therefore set out to test whether baseline serum CRP levels are associated with mortality in four different ILDs. Methods In this retrospective study, clinically measured CRP levels, as well as baseline demographics and lung function measures, were collected for ILD patients first presenting to the Royal Brompton Hospital between January 2010 and December 2019. Cox regression analysis was used to determine the relationship with 5‐year mortality. Results Patients included in the study were: idiopathic pulmonary fibrosis (IPF) n = 422, fibrotic hypersensitivity pneumonitis (fHP) n = 233, rheumatoid arthritis associated ILD (RA‐ILD) n = 111 and Systemic Sclerosis associated ILD (SSc‐ILD) n = 86. Patients with a recent history of infection were excluded. Higher CRP levels were associated with shorter 5‐year survival in all four disease groups on both univariable analyses, and after adjusting for age, gender, smoking history, immunosuppressive therapy and baseline disease severity (IPF: HR (95% CI): 1.3 (1.1–1.5), p = 0.003, fHP: 1.5 (1.2–1.9), p = 0.001, RA‐ILD: 1.4 (1.1–1.84), p = 0.01 and SSc‐ILD: 2.7 (1.6–4.5), p < 0.001). Conclusion Higher CRP levels are independently associated with reduced 5‐year survival in IPF, fHP, RA‐ILD and SSc‐ILD.