Evaluation of Serum IL-39 Levels in Patients with Polycystic Ovary Syndrome

Background/Objectives: Polycystic ovary syndrome (PCOS) is a common endocrine disorder associated with chronic low-grade inflammation. Interleukin-39 (IL-39), a newly identified cytokine, has been implicated in immune regulation; however, its role in PCOS remains unclear. This study aimed to evaluate serum IL-39 levels in patients with PCOS and its potential as an adjunctive inflammatory biomarker candidate. Methods: This case-control study included 44 patients with PCOS diagnosed according to the Rotterdam criteria and 44 age-matched in the control group. Serum IL-39 levels were measured using enzyme-linked immunosorbent assay (ELISA). Clinical and laboratory parameters were recorded. Group comparisons were performed using appropriate parametric and non-parametric tests. Correlation analysis was conducted using Spearman's coefficient. Multivariable logistic regression analysis was performed to identify independent predictors of PCOS. Receiver operating characteristic (ROC) analysis was used to assess discriminative performance. Results: Serum IL-39 levels were significantly higher in the PCOS group compared to control group (p < 0.001). No significant correlations were observed between IL-39 and other clinical or laboratory parameters. In multivariable analysis, IL-39 was independently associated with PCOS. ROC analysis showed that IL-39 had moderate discriminative ability (AUC = 0.74), with 68% sensitivity and 70% specificity. The combined model including IL-39, body mass index (BMI), luteinizing hormone (LH), and age demonstrated improved performance (AUC = 0.78), with higher sensitivity (86%) and negative predictive value (81%). Conclusions: IL-39 levels are elevated in PCOS and may represent a potential adjunctive inflammatory biomarker candidate. Its diagnostic performance improves when combined with other clinical parameters, supporting a multivariable approach in PCOS evaluation.