Women with polycystic ovary syndrome have intrinsic insulin resistance on euglycaemic-hyperinsulaemic clamp

STUDY QUESTION: What is the prevalence of insulin resistance (IR) and the contributions of intrinsic and extrinsic IR in women diagnosed with polycystic ovary syndrome (PCOS) according to the Rotterdam criteria? SUMMARY ANSWER: We report novel clamp data in Rotterdam diagnosed PCOS women, using World Health Organization criteria for IR showing that women with PCOS have a high prevalence of IR, strengthening the evidence for an aetiological role of IR in both National Institutes of Health (NIH) and Rotterdam diagnosed PCOS in lean and overweight women. WHAT IS KNOWN ALREADY: PCOS is a complex endocrine condition with a significant increased risk of gestational diabetes and type 2 diabetes. STUDY DESIGN, SIZE, DURATION: Using a cross-sectional study design, 20 overweight and 20 lean PCOS (Rotterdam criteria), 14 overweight and 19 lean body mass index (BMI)-matched control non-PCOS women underwent clinical measures of IR after a 3-month withdrawal of insulin sensitizers and the oral contraceptive pill. MATERIALS, SETTING, METHODS: In an academic clinic setting, glucose infusion rate (GIR) on euglycaemic-hyperinsulinaemic clamp was investigated as a marker of insulin sensitivity. MAIN RESULTS AND THE ROLE OF CHANCE: PCOS women were more IR than BMI-matched controls (main effect for BMI and PCOS; P < 0.001). IR was present in 75% of lean PCOS, 62% of overweight controls and 95% of overweight PCOS. Lean controls (mean ± SD; GIR 339 ± 76 mg min⁻¹ m⁻²) were less IR than lean PCOS (270 ± 66 mg min⁻¹ m⁻²), overweight controls (264 ± 66 mg min⁻¹ m⁻²) and overweight PCOS (175 ± 96 mg min⁻¹ m⁻²). The negative relationship between BMI and IR reflected by GIR was more marked in PCOS (y = 445.1 - 7.7x, R² = 0.42 (P < 0.0001) than controls (y = 435.5 - 4.6x, R² = 0.04 (P