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

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. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s10157-020-01879-8) contains supplementary material, which is available to authorized users.