Objective:To establish a scoring model with complement C3 to evaluate insulin sensitivity(IS)in polycystic ovary syndrome(PCOS)population. Methods:Ninety-nine PCOS patients and 116 age-matched healthy women were included in this study. Anthropometric parameters and fasting biochemical indicators(including insulin

hs-CRP

complement C3

etc.)were determined and homeostasis model assessment of insulin resistance(HOMA2-IR)was calculated. All PCOS patients and 20 healthy controls underwent hyperinsulinemic-euglycemic clamp assay. The equation of IS score was established by multiple liner regression among PCOS patients

and the value of this equation for IR diagnosis was assessed according to the ROC curve. Results:The IS score=19.36-0.35×BMI-2.28 ×C3(R2=0.54

P =0.000). Areas under the ROC curve of IS score and HOMA2-IR were 0.89(0.83 to 0.96) and 0.75(0.64 to0.86)respectively. The sensitivity and specificity of IS score were 0.70 and 0.95

and Youden index equaled to 0.63. The sensitivity and specificity of HOMA2-IR were 0.6 and 0.88

and Youden index equaled to 0.47. Conclusion:IS scoring model with complement C3 is valuable for the diagnosis of IR in PCOS population.