The Cutoff Value of Low Sex Hormone-Binding Globulin and Its Predictive Role in Impaired Glucose Metabolism Among Chinese Women with Polycystic Ovarian Syndrome

Background: Low levels of sex hormone-binding globulin (SHBG) is a potential predictor of type 2 diabetes mellitus (T2DM), and when combined with insulin resistance (IR), lead to impaired glucose metabolism. Few studies involve women with polycystic ovarian syndrome (PCOS). Studies on cutoff values of SHBG among Asian women were scanty. Methods: The cutoff level of SHBG was computed using the 25th percentile method. Parameters were compared between the lower and higher SHBG subgroup. Area under the curve (AUC) for sensitivity and specificity of SHBG in predicting IR and impaired glucose metabolism was calculated. Results: This study included 733 patients with PCOS 20-45 years of age and 469 age-matched controls. The 25th percentile of SHBG in the control group was 51.90 nM. There were negative correlations between SHBG and age (r = -0.085, P < 0.05), body mass index (BMI) (r = -0.461, P < 0.01), waist-to-hip ratio (WHR) (r = -0.349, P < 0.01), fasting plasma glucose (r = -0.242, P < 0.01), Glucose-1h (r = -0.303, P < 0.01), Glucose-2h (r = -0.336, P < 0.01), fasting insulin (r = -0.324, P < 0.01), Insulin-1h (r = -0.238, P < 0.01), Insulin-2h (r = -0.307, P < 0.01), and homeostasis model 2 assessment of insulin resistance (HOMA2-IR) (r = -0.329, P < 0.01). Age, BMI, WHR, glucose and insulin levels (both pre- and postload), HOMA2-IR, free testosterone, and dehydroepiandrosterone sulfate were all higher in the lower than the higher SHBG subgroup. The AUC of SHBG for predicting IR was 0.706 [95% confidence interval (CI) 0.665-0.745, P < 0.001], impaired fasting glucose was 0.674 (95% CI 0.513-0.838, P < 0.001), impaired glucose tolerance was 0.637 (95% CI 0.586-0.690, P < 0.001), and T2DM was 0.674 (95% CI 0.556-0.780, P < 0.001). Conclusions: A 51.90 nM should be identified as the cutoff value of SHBG. Women with PCOS with lower SHBG values have a higher risk of developing impaired glucose metabolism. Low SHBG should be a predictive biomarker of impaired glucose metabolism in women with PCOS in southern China.