Circulating Fatty Acid-Binding Protein 4 (FABP4) in Adolescents with Polycystic Ovary Syndrome: Metabolic Correlates and Diagnostic Performance.

To compare circulating fatty acid-binding protein 4 (FABP4) concentrations in adolescents with polycystic ovary syndrome (PCOS) and controls, examine its metabolic correlates, and evaluate its diagnostic performance. This prospective observational study included 88 adolescents (44 PCOS, 44 controls) aged 10-19 years. PCOS was diagnosed using 2023 ESHRE/ASRM criteria. Clinical, anthropometric, and biochemical parameters were assessed. Serum FABP4 was measured via ELISA. Statistical analyses included multivariable linear regression, Firth's penalized logistic regression, and receiver operating characteristic (ROC) curves. Median FABP4 levels were significantly higher in adolescents with PCOS compared to controls (5.74 vs. 3.59 ng/mL, p < 0.001). Multivariable linear regression demonstrated that PCOS status, body mass index (BMI), and insulin resistance (HOMA-IR) associated with higher FABP4 concentrations. Multivariable logistic regression identified free androgen index (FAI) and FABP4 as variables independently associated with PCOS. ROC analysis showed FABP4 (> 4.08 ng/mL) yielded an area under the curve (AUC) of 0.849 (81.8% sensitivity, 75.0% specificity). The combination of FABP4 and FAI improved model discrimination compared with FAI alone (ΔAUC = 0.133, p = 0.001), and this improvement remained significant after BMI adjustment. Circulating FABP4 is elevated in adolescents with PCOS and is associated with PCOS status, BMI, and insulin resistance. In this cohort, FABP4 provided complementary metabolic information when interpreted alongside FAI; however, BMI-matched, body composition-characterized, and externally validated studies are needed before FABP4 can be considered a clinically generalizable adjunctive biomarker in adolescent PCOS.