Geovariation in Fracture Risk among Patients Receiving Hemodialysis.

Abstract

Fractures are a major source of morbidity and mortality in patients receiving dialysis. We sought to determine whether rates of fractures and tendon ruptures vary geographically. Data from the US Renal Data System were used to create four yearly cohorts, 2007-2010, including all eligible prevalent patients on hemodialysis in the United States on January 1 of each year. A secondary analysis comprising patients in a large dialysis organization conducted over the same period permitted inclusion of patient-level markers of mineral metabolism. Patients were grouped into 10 regions designated by the Centers for Medicare and Medicaid Services and divided by latitude into one of three bands: south, <35°; middle, 35° to <40°; and north, ≥40°. Poisson regression was used to calculate unadjusted and adjusted region-level rate ratios for events. Overall, 327,615 patients on hemodialysis were included. Mean (SD) age was 61.8 (15.0) years old, 52.7% were white, and 55.0% were men. During 716,962 person-years of follow-up, 44,014 fractures and tendon ruptures occurred, the latter being only 0.3% of overall events. Event rates ranged from 5.36 to 7.83 per 100 person-years, a 1.5-fold rate difference across regions. Unadjusted region-level rate ratios varied from 0.83 (95% confidence interval, 0.81 to 0.85) to 1.20 (95% confidence interval, 1.18 to 1.23), a 1.45-fold rate difference. After adjustment for a wide range of case mix variables, a 1.33-fold variation in rates remained. Rates were higher in north and middle bands than the south (north rate ratio, 1.18; 95% confidence interval, 1.13 to 1.23; middle rate ratio, 1.13; 95% confidence interval, 1.10 to 1.17). Latitude explained 11% of variation, independent of region. A complementary analysis of 87,013 patients from a large dialysis organization further adjusted for circulating mineral metabolic parameters and protein energy wasting yielded similar results. Rates of fractures vary geographically in the United States dialysis population, even after adjustment for known patient characteristics. Latitude seems to contribute to this phenomenon, but additional analyses exploring whether other factors might influence variation are warranted.