Mineral metabolism and outcomes in chronic kidney disease stage 2-4 patients.

Background: Marked hyperphosphatemia, hyperparathyroidism and 25-hydroxyvitamin D deficiency are associated with mortality in dialysis patients. Such data in chronic kidney disease stage 2-4 population are limited. It has been suggested that high-normal serum phosphate predicts worse renal and patient outcomes. The data regarding parathyroid hormone and outcomes in this population is limited. The present study examined mineral metabolism and its association with the development of end-stage renal disease and mortality in stage 2-4 chronic kidney disease patients.

Methods: This is a prospective cohort study that included 466 non-dialysis chronic kidney disease stage 2-4 patients. Mineral parameters were obtained at the time of enrollment and the patients were followed prospectively for 25 (1-44) months or until they reached the endpoints of end-stage renal disease or mortality.

Results: Hyperparathyroidism and 25-hydroxyvitamin D deficiency began to occur in the early stages of chronic kidney disease, whereas significant hyperphosphatemia only developed in the later stages. High-normal and mildly elevated serum phosphate (>4.2 mg/dL) predicted the composite outcome of end-stage renal disease or mortality after adjustments for cardiovascular risk factors, chronic kidney disease stage and other mineral parameters. Parathyroid hormone levels above the upper limit of normal (>65 pg/mL) predicted the future development of end-stage renal disease and the composite outcome of end-stage renal disease or mortality after adjustments. 25-hydroxyvitamin D deficiency (<15 ng/mL) was also associated with worse outcomes.

Conclusions: In chronic kidney disease, hyperparathyroidism developed prior to significant hyperphosphatemia confirming the presence phosphate retention early in the course of chronic kidney disease. High-normal serum phosphate and mildly elevated parathyroid hormone levels predicted worse renal and patient outcomes. This data emphasizes the need for early intervention in the care of chronic kidney disease stage 2-4 patients.