Differentiating PCOS from Anovulatory Cycles in Adolescents: A Comprehensive Evaluation of FAI, SHBG, and LH/FSH Ratio

Background Menstrual irregularities are common among adolescents, often linked to anovulatory cycles. This study aims to establish diagnostic cut-off values for Polycystic Ovary Syndrome (PCOS) and differentiate these from anovulatory dysfunction in adolescents. Additionally, we assessed the sensitivity of using the Free Androgen Index (FAI) and Sex Hormone Binding Globulin (SHBG) in diagnosing PCOS. Methods This study included 305 adolescents presenting with oligomenorrhea at a tertiary center. Data were analyzed statistically and Receiver operating characteristic (ROC) curves were plotted to evaluate diagnostic performance. Results Of the 305 patients, 229 (75%) had anovulatory cycles and 36 (11.8%) had PCOS. The mean FAI values for anovulatory cycles, PCOS, and hyperinsulinism were 3.5 ± 2, 8.0 ± 5, and 8.3 ± 4, respectively (p < 0.001). A significant positive correlation was found between FAI and both HOMA-IR (r = 0.389; p < 0.001) and BMI (r = 0.499; p < 0.001). ROC analysis determined the LH threshold of 9.7 U/L and LH/FSH ratio threshold of 2.62 as predictive markers for PCOS. Conclusions Anovulatory cycles are the most frequent cause of menstrual irregularities in adolescents, with hyperandrogenism being crucial for diagnosing PCOS. The FAI may be unreliable for PCOS diagnosis due to similar values in adolescents with hyperinsulinemia and obesity. Lower SHBG levels in hyperinsulinemic obese adolescents further complicate the use of FAI, indicating that glucose/insulin metabolism significantly influences FAI/SHBG levels. Comprehensive diagnostic criteria, including androgen levels, LH/FSH ratio, SHBG, FAI levels, and ovarian ultrasound, are essential for accurate PCOS diagnosis.