Biomarkers in sarcoidosis: a review

Hasib Ahmadzai,^1,2 Wei Sheng Joshua Loke,¹ Shuying Huang,¹ Cristan Herbert,¹ Denis Wakefield,³ Paul S Thomas<sup>2

1</sup>Inflammation and Infection Research Centre (IIRC), Faculty of Medicine, University of New South Wales, Sydney, NSW, Australia; ²Department of Respiratory Medicine, Prince of Wales Hospital, Randwick, Sydney, NSW, Australia; ³Immunology of the Eye Clinic, St Vincent's Clinic, Darlinghurst, Sydney, NSW, Australia

Abstract: Sarcoidosis is a systemic granulomatous disease of undetermined etiology invariably affecting the lungs and thoracic lymph nodes. It has been termed an “immune paradox”, as there is peripheral anergy despite exaggerated inflammation at disease sites. The disease is usually self-limiting, although some individuals experience unremitting inflammation that may progress into pulmonary fibrosis and death. The inflammatory process is largely a T helper-1-driven immune response. Given its heterogeneous clinical manifestations, diagnosis is usually a clinical conundrum. Clinical and radiological findings alone are often inadequate to confirm the diagnosis. At present, sarcoidosis is usually a diagnosis of exclusion, confirmed by histological evidence of noncaseating granulomas in the absence of known granulomagenic agents. This has compelled researchers to look for disease-specific biomarkers that can help diagnose sarcoidosis and delineate its disease course, severity, and prognosis. In this review we highlight various investigations used to diagnose sarcoidosis, outline proposed biomarkers, and discuss novel methods of sampling biomarkers.

Keywords: sarcoidosis, biomarkers, inflammatory markers, exhaled breath condensate, proteomics, granuloma