Peripheral Blood Biomarkers for Rheumatoid Arthritis–Associated Interstitial Lung Disease: A Systematic Review

BACKGROUND: Biomarkers have been proposed as tools to aid in the identification and prognostication of interstitial lung disease (ILD) in rheumatoid arthritis (RA). We performed a systematic review of studies evaluating peripheral blood biomarkers and their association with RA‐ILD and its prognosis. METHODS: Medline, Embase, the Cochrane Library, and Scopus were queried for relevant studies, with the final search update on July 12, 2021. We included studies evaluating peripheral blood biomarkers for the identification and/or prognostication of RA‐ILD, extracting the performance of individual biomarkers for identifying RA‐ILD, and predicting prognosis. Modified versions of the Quality Assessment of Diagnostic Accuracy Studies 2 and the Quality in Prognosis Studies tools were used for quality assessment. RESULTS: Seventy studies met eligibility criteria. Study and patient characteristics, analytical methods, strength and consistency of associations, and study quality were heterogeneous. A total of 92 biomarkers were positively associated and 12 were negatively associated with RA‐ILD among patients with RA in one or more report. Only a small number of biomarkers were evaluated in multiple cohorts using adjusted analyses. Biomarkers most strongly associated with RA‐ILD overlapped with those identified for idiopathic pulmonary fibrosis. Few prognostic biomarkers of RA‐ILD were identified. CONCLUSION: Several peripheral blood biomarkers are associated with the presence of RA‐ILD, but few have been assessed in multivariable models, have been externally validated, have discriminated RA‐ILD from other lung disease, or have prognosticated the disease course. High‐quality studies investigating and validating peripheral biomarkers in RA‐ILD are needed before they can be employed in clinical care.