Relationship between serum calcium or phosphate levels and mortality stratified by parathyroid hormone level: an analysis from the MBD-5D study

Abstract

Introduction: There is limited evidence about the association between calcium and phosphate levels and mortality stratified by intact parathyroid hormone (iPTH) level.

Methods: We investigated whether differences in iPTH level affect the relationship between calcium and phosphate levels and all-cause mortality in hemodialysis patients with secondary hyperparathyroidism (SHPT). Calcium and phosphate levels were categorized as low (< 8.5 mg/dL, < 4.0 mg/dL), medium (≥ 8.5-< 9.5 mg/dL, ≥ 4.0-< 7.0 mg/dL), and high (≥ 9.5 mg/dL, ≥ 7.0 mg/dL), respectively. iPTH levels were grouped into < 300 or ≥ 300 pg/mL. Adjusted incidence rate ratios (aIRRs) were analyzed by weighted Poisson regression.

Results: For calcium, patients with higher iPTH (≥ 300 pg/mL) had significantly higher all-cause mortality rates in the high than in the medium category (aIRR 1.99, 95% confidence interval [CI] 1.16-3.42), and tended to have a higher mortality rate in the low category (aIRR 2.04, 95% CI 0.94-4.42). Patients with lower iPTH (< 300 pg/mL) had higher mortality rates in the high than in the medium category (aIRR 1.65, 95% CI 1.39-1.96). For phosphate, the mortality rate was significantly higher in the high than in the medium category in patients with higher and lower iPTH (aIRR 3.23, 95% CI 1.63-6.39 for iPTH ≥ 300 pg/mL; aIRR 1.58, 95% CI 1.06-2.36 for iPTH < 300 pg/mL).

Conclusion: High calcium and phosphate levels were associated with increased risk of mortality irrespective of iPTH level.

Keywords: Calcium; Chronic kidney disease–mineral and bone disorder; Hemodialysis; Mortality; Parathyroid hormone; Phosphate.

Fig. 1

Adjusted incidence rate for all-cause mortality (a) and cardiovascular mortality (b) stratified by levels of serum intact parathyroid hormone and serum calcium. Ca calcium, iPTH intact parathyroid hormone. Incidence rate ratios were adjusted for patients’ characteristics (age, sex, primary kidney disease, diabetes, dialysis duration, cardiovascular disease, pulmonary disease, liver disease, malignancy, and history of parathyroidectomy) and time-dependent variables (vitamin D receptor activators, phosphate binders, calcimimetics, serum albumin level, hemoglobin level, body mass index, Kt/V, and dialysate calcium concentration)

Fig. 2

Adjusted incidence rate for all-cause mortality (a) and cardiovascular mortality (b) stratified by levels of serum intact parathyroid hormone and serum phosphate. iPTH intact parathyroid hormone, P phosphate. Incidence rate ratios were adjusted for patients’ characteristics (age, sex, primary kidney disease, diabetes, dialysis duration, cardiovascular disease, pulmonary disease, liver disease, malignancy, and history of parathyroidectomy) and time-dependent variables (vitamin D receptor activators, phosphate binders, calcimimetics, serum albumin level, hemoglobin level, body mass index, Kt/V, and dialysate calcium concentration)