Endocrine Abstracts

JOINT1632

Introduction: Reference intervals for serum total testosterone (TT), free testosterone (FT), and sex hormone-binding globulin (SHBG) are essential for diagnosing hypogonadism in men. Obesity influences androgen and SHBG concentrations, complicating the interpretation of hormonal changes. This study aims to establish reference intervals for serum TT, FT, and SHBG in middle aged adults and to calculate expected values for different BMI categories.

Methods: The Netherlands Epidemiology of Obesity study is a population-based prospective cohort study comprising 3156 male participants aged 45–65, with oversampling of individuals with a BMI >25kg/m². Fasting blood samples were analysed for testosterone and SHBG concentrations using LC–MS/MS and an automated immunoassay (Architect), respectively. FT was calculated using the Vermeulen formula. The reference population was defined by a BMI <25kg/m², no history of cardiovascular or hormone-affecting diseases, non-smokers, and no use of medication. Reference intervals were calculated, based on the 2.5th and 97.5th percentiles, for testosterone, SHBG, and free testosterone. The proportions of individuals of BMI groups falling within the reference intervals were assessed.

Results: Reference intervals for 216 men aged 45-65 years with a BMI <25 kg/m² were 8.3 – 28.7 nmol/l for TT, 139 – 422 pmol/l for FT, and 17.7 – 80.8 nmol/l for SHBG. As BMI increases, a greater proportion of men fall below the lower limit of the reference intervals. Specifically, among men with a BMI >35 kg/m², 24% fall below the reference interval for TT, 17% for FT and 11% for SHBG.

Conclusion: We present reference intervals for TT, FT and SHBG in middle-aged men. Men with overweight or obesity more often fall outside these reference intervals. Our findings can improve interpretation of abnormal laboratory results in individuals with overweight or obesity.