Assessment of calcium balance in patients on hemodialysis, based on ionized calcium and parathyroid hormone responses.

Background: Identification of the underlying causes of secondary hyperparathyroidism (SHPT) in individual patients on hemodialysis (HD) is hampered by the lack of clinically reliable information on calcium balance. The aim of this study was to assess calcium balance during HD sessions with a method that is applicable in day-to-day practice.

Methods: Plasma ionized calcium (pCa2+) and parathyroid hormone (PTH) were measured at the beginning and end of HD to evaluate calcium fluxes in 23 patients on a dialysate calcium (DCa) concentration of 1.25 mmol/L.

Results: HD with a DCa of 1.25 mmol/L caused a decrease in pCa2+ from 1.15 ± 0.01 mmol/L to 1.09 ± 0.01 mmol/L (p<0.0001) and increased plasma PTH from 26.7 ± 1.8 pmol/L to 37.0 ± 2.9 pmol/L (p<0.0001). The changes in pCa2+ were inversely related to the predialysis pCa2+ levels (R2 = 0.86, p<0.001). Patients with a predialysis pCa2+ >1.06 mmol/L had a calcium efflux, whereas those with a predialysis pCa2+ <1.06 mmol/L had a calcium influx during HD.

Conclusion: The results suggest that measurement of pCa2+ and PTH at the beginning and the end of HD provides useful information about calcium fluxes in individual patients. Further validation of this approach 
is warranted.