Abstract
KDIGO guidelines recommend dietary phosphate restriction to lower serum phosphate levels in CKD stages 3-5. Recent studies suggest that dietary phosphate intake is only weakly linked to its serum concentration, and the relationship of phosphate intake with adverse outcomes is uncertain. To evaluate this, we used Cox proportional hazards models to assess associations of baseline 24-h urine phosphate excretion with risk of end-stage renal disease (ESRD), all-cause mortality, and mortality subtypes (cardiovascular disease [CVD] and non-CVD) using the Modification of Diet in Renal Disease data. Models were adjusted for demographics, CVD risk factors, iothalamate GFR, and urine protein and nitrogen excretion. Phosphate excretion was modestly inversely correlated with serum phosphate concentrations. There was no association of 24-h urinary phosphate excretion with risk of ESRD, CVD, non-CVD, or all-cause mortality. For comparison, higher serum phosphate concentrations were associated with all-cause mortality (hazard ratio per 0.7 mg/dl higher, 1.15 [95% CI 1.01, 1.30]). Thus, phosphate intake is not tightly linked with serum phosphate concentrations in CKD stages 3-5, and there was no evidence that greater phosphate intake, assessed by 24-h phosphate excretion, is associated with ESRD, CVD, non-CVD, or all-cause mortality in CKD stages 3-5. Hence, factors other than dietary intake may be key determinants of serum phosphate concentrations and require additional investigation.