Interaction between phosphorus and parathyroid hormone in non-dialysis CKD patients under nephrology care

Whether the traditional treatment of chronic kidney disease (CKD)-mineral and bone disorder is effective in the setting of tertiary nephrology care is an unexplored question. We evaluated phosphate, calcium and PTH levels during the first year of nephrology care and the prognostic role of month-12 levels in non-dialysis patients referred prior to availability of the novel P binders.

We studied a historical cohort of consecutive patients with CKD stage 3-5 at referral (baseline), and after 6 and 12 months of nephrology care; thereafter, patients were followed for renal survival (time to death or end-stage renal disease).

At month 12, versus baseline, we detected a larger implementation of dietary protein restriction (P = 0.001), vitamin D and P binder (P < 0.0001 for both). Mean serum P remained unchanged (4.02 ± 0.77, 4.01 ± 0.79, 4.10 ± 0.85 mg/dL at baseline, month 6 and 12, respectively) with only 18, 16 and 21 % patients showing uncontrolled serum P at the three study visits. Similarly, calcium levels were unchanged and within the target in most cases. Conversely, intact PTH increased from 102 pg/mL (interquartile range 67-139) to 113 (68-179), P = 0.015, with 59, 60 and 53 % patients showing high values at the three study visits. During the subsequent follow-up (31 months), 96 renal deaths occurred. Cox analysis evidenced a significant prognostic role of the interaction P × PTH (P = 0.002), that is, the risk of renal death associated with serum P increased in the presence of higher PTH.

In patients under nephrology care, P and PTH should be considered in concert to optimize risk stratification for renal death.