Supplementary Material for: Race, Mineral Homeostasis and Mortality in Patients with End-Stage Renal Disease on Dialysis

<b><i>Background:</i></b> Abnormalities in mineral homeostasis are ubiquitous in patients on dialysis, and influenced by race. In this study, we determine the race-specific relationship between mineral parameters and mortality in patients initiating hemodialysis. <b><i>Methods:</i></b> We measured the levels of fibroblast growth factor 23 (FGF23) and 25-hydroxyvitamin D (25 D) in 184 African American and 327 non-African American hemodialysis patients who enrolled between 1995 and 1998 in the Choices for Healthy Outcomes in Caring for ESRD Study. Serum calcium, phosphorus, parathyroid hormone (PTH) and total alkaline phosphatase levels were averaged from clinical measurements during the first 4.5 months of dialysis. We evaluated the associated prospective risk of mortality using multivariable Cox proportional hazards models stratified by race. <b><i>Results:</i></b> PTH and total alkaline phosphatase levels were higher, whereas calcium, phosphorus, FGF23 and 25 D levels were lower in African Americans compared to those of non-African Americans. Higher serum phosphorus and FGF23 levels were associated with greater mortality risk overall; however, phosphorus was only associated with risk among African Americans (HR 5.38, 95% CI 2.14-13.55 for quartile 4 vs. 1), but not among non-African Americans (p-interaction = 0.04). FGF23 was associated with mortality in both groups, but more strongly in African Americans (HR 3.91, 95% CI 1.74-8.82 for quartiles 4 vs. 1; p-interaction = 0.09). Serum calcium, PTH, and 25 D levels were not consistently associated with mortality. The lowest and highest quartiles of total alkaline phosphatase were associated with higher mortality risk, but this did not differ by race (p-interaction = 0.97). <b><i>Conclusions:</i></b> Aberrant phosphorus homeostasis, reflected by higher phosphorus and FGF23, may be a risk factor for mortality in patients initiating hemodialysis, particularly among African Americans.