Impact of age on survival predictability of bone turnover markers in hemodialysis patients

Abnormalities in serum alkaline phosphatase (ALP) and intact parathyroid hormone (PTH) concentrations, as biochemical markers of bone turnover in dialysis patients, correlate with increased mortality in maintenance hemodialysis (MHD) patients. Changes in bone turnover rate vary with age. The mortality predictability of serum ALP and PTH levels in MHD patients may be different across ages. We examined differences across four age groups (18 to 45, 45 to 65, 65 to 75 and 75 years) in the mortality predictability of serum ALP and PTH in 102 149 MHD patients using Cox models. Higher serum ALP levels were associated with higher mortality across all ages; however, the ALPmortality association was much stronger in young patients (45 years) compared with older patients. The association between higher serum PTH levels and mortality was stronger in older patients compared with the younger groups. Serum PTH levels were incrementally associated with mortality only in middle-aged and elderly patients (45 years). Compared with patients with serum PTH 150 to 300pg/mL, the death risks were higher in patients with serum PTH 300 to 600pg/mL [HRs (95 CI): 1.05 (1.011.10), 1.15 (1.101.21) and 1.25 (1.191.31) for patients 45 to 65, 65 to 75 and 75 years, respectively], and 600pg/mL [HRs(95 CI): 1.07 (1.011.14), 1.31(1.211.42) and 1.45(1.331.59) for age categories 45 to 65, 65 to 75 and 75 years, respectively]. However, no significant association between higher serum PTH levels and mortality was observed in patients 45 years. There are important differences in mortality-predictability of serum ALP and PTH in older MHD patients compared with their younger counterparts. The effect of age needs to be considered when interpreting the prognostic implications of serum ALP and PTH levels.