Prognosis and determinants of serum PTH changes over time in 1-5 CKD stage patients followed in tertiary care

International Guidelines for mineral bone disorders recommend that in Non Dialytic-Chronic Kidney Disease (ND-CKD) clinical decisions should be based on the trend of serum PTH changes over time rather than on a single value. However, the prognostic impact of these changes in ND-CKD patients remains unknown. We performed a multicenter cohort study in ND-CKD patients (stage 1-5) followed for 36 months in 24 Italian Nephrology Units. PTH changes (ΔPTH) were defined as the absolute differences between all available PTH measurements following the first control and basal value. Primary endpoint in this subanalysis was renal death (End-Stage Renal Disease (ESRD) or all-causes death before ESRD). Association between renal death and ΔPTH was assessed by time-dependent Cox model for repeated measurements. Out of the original cohort (N = 884), we selected 543 patients (66.3±15.4 ys, 58.4% males) with at least two serum PTH measurements. At baseline, eGFR was 36 (IQR: 22.4-56.8) mL/min/1.73m2 and serum PTH 46 (IQR: 28-81) pg/mL. ΔPTH was in median 0 (IQR:-18/18) pg/mL. Basal predictors of longitudinal PTH increments were higher serum phosphate, more advanced CKD stages and lower serum PTH. Fully adjusted Cox model with ΔPTH quartiles as discrete time-dependent covariate showed a significant risk of renal death in the highest quartile (HR: 1.91; 95%CI:1.08-3.38; P = 0.026). Considering ΔPTH, as continuous time-dependent variable, (HR:1.02; 95%C.I.: 1.01-1.04; P = 0.004), risk of renal death progressively rose as ΔPTH increased. An increment in serum PTH over time is associated with a worse prognosis in ND-CKD patients, independently from baseline or any absolute concentration of serum PTH and phosphate.