Bioavailable Testosterone Is Positively Associated With Bone Mineral Density in Male Kidney Transplantation Candidates

INTRODUCTION: Low levels of sex hormones are common in patients with chronic kidney disease (CKD) and may be a contributing factor to bone fragility. We investigated associations between levels of sex hormones and bone mineral density (BMD) in adult kidney transplantation candidates. METHODS: Volumetric BMD of spine and hip were measured by computed tomography. Parathyroid hormone (PTH), testosterone (T), estradiol (E), and sex hormone–binding globulin were measured from fasting morning blood samples. Bioavailable (Bio) T and E were calculated based on constants for protein binding. RESULTS: A total of 146 patients (102 men and 44 women) were included in the analyses. The median age was 54 years (range, 32−72 years); 32% were diabetic; and 36% received maintenance dialysis therapy. In men, Bio T was positively associated with BMD at the lumbar spine (β = 5.02, P = 0.002), total hip (β = 6.35, P = 0.001), and femoral neck (β = 13.9, P = 0.002), independently of age, body mass index, dialysis, diabetes type 1 and 2, parathyroid hormone, and steroid exposure. Bio E was positively associated with BMD at the lumbar spine (β = 0.23, P = 0.03) and femoral neck (β = 0.61, P = 0.04) using the same fully adjusted model. In postmenopausal women, Bio T was positively correlated with lumbar spine BMD (r = 0.46, P = 0.02). CONCLUSION: High endogenous levels of sex hormones are associated with greater BMD in male kidney transplantation candidates. Disturbances in the gonadal axis may contribute to skeletal fragility in men with late-stage CKD.