The mean change in serum phosphate was -1.29 mg/dl ( 95 % confidence interval , -1.63 to -0.96 mg/dl ) in the ferric citrate hydrate group and 0.06 mg/dl ( 95 % confidence interval , -0.20 to 0.31 mg/dl ) in the placebo group ( P < 0.001 for difference between groups ) .