Determinants of bone mineral density in stable kidney transplant recipients

Background: Kidney transplant recipients (KTR) are at increased risk for bone loss. Determinants of bone mineral density (BMD) in an unselected KTR population have not previously been described. Methods: We conducted a cross-sectional analysis of 389 stable KTRs undergoing bone mineral densitometry assessment by dual-energy X-ray absorptiometry at the lumbar spine, total hip and femoral neck. Risk factors for osteopenia and osteoporosis were determined by t-tests or ANOVA and chi-square analysis as appropriate. Factors associated with reduced BMD were ascertained using multivariate linear regression. Results: At the lumbar spine, 247 demonstrated normal BMD, 115 had osteopenia and 27 osteoporosis. Corresponding prevalence rates for the total hip and femoral neck were 222/143/24 and 178/184/27, respectively. Osteopenia or osteoporosis was more prevalent at the femoral neck than lumbar spine (p=0.002). Osteopenia or osteoporosis at the spine, hip and femoral neck were highly correlated (p<0.0001). Independent associations with reduced BMD included female sex (p<0.0001) and lower body mass index (p<0.0001) at all sites, age for total hip and femoral neck (p=0.0001), and hyperparathyroidism (p=0.036), time posttransplant (p=0.0001) for the femoral neck, with no association by renal function or 25-OH vitamin D level at any site. Conclusions: Significant bone loss in KTRs is most prevalent at the femoral neck. Identifying risk factors for specific sites may allow for earlier intervention prior to osteoporosis development.