Value of serum soluble interleukin-2 receptor as a diagnostic and predictive biomarker in sarcoidosis

Background: Differentiating between interstitial lung diseases (ILD) is challenging. Serum soluble interleukin 2 receptor (sIL-2R) is used as a diagnostic marker in sarcoidosis, but its diagnostic value has not yet been studied in other ILDs like Idiopathic Pulmonary Fibrosis (IPF) or Hypersensitivity Pneumonitis (HP). Also, the prognostic value of sIL-2R in sarcoidosis remains unknown. Methods: This retrospective cohort study included 121 patients with sarcoidosis, 35 with cHP, 62 with IPF (idiopathic pulmonary fibrosis) and 70 healthy controls. Serum sIL-2R levels were determined at diagnosis. Follow-up data were available for patients with chronic sarcoidosis (n = 64) and patients with non-chronic sarcoidosis (n = 29). Results: Patients with sarcoidosis had higher sIL-2R levels (median 5418 pg/mL) than patients with cHP (median 4015 pg/mL, P = 0.002) and IPF (median 4192 pg/mL, P = 0.034). No differences were found between patients with cHP and IPF. Logistic regression revealed that sIL-2R at diagnosis is a significant predictor of the development of chronic sarcoidosis (OR = 2.1, P = 0.032). Conclusion: High levels of sIL-2R are suggestive of sarcoidosis, although a broad overlap exists in sIL-2R levels across sarcoidosis, cHP, and IPF. High levels of sIL-2R might serve as a prognostic biomarker for chronicity.