Dialysis – Transplantation
Kidney International (1998) 54, 2140–2145; doi:10.1046/j.1523-1755.1998.00221.x
Effect of serum phosphate on parathyroid hormone secretion during hemodialysis
Angel L M de Francisco, Maria A Cobo, Maria A Setien, Emilio Rodrigo, Gema F Fresnedo, Maria T Unzueta, Jose A Amado, J Carlos Ruiz, Manuel Arias and Mariano Rodriguez
Nephrology and Endocrinology Division, Hospital Universitario Valdecilla, Santander, and Nephrology Division and Research Unit, Hospital Reina Sofia, University of Cordoba, Cordoba, Spain
Correspondence: Dr Angel L.M. de Francisco, Servicio de Nefrología, Hospital Universitario de Valdecilla, Avda Valdecilla, s/n, Santander, 39008, Spain. E-mail: martinal@medi.unican.es
Received 5 December 1997; Revised 15 July 1998; Accepted 16 July 1998.
Abstract
Effect of serum phosphate on parathyroid hormone secretion during hemodialysis.
Background
Recent studies have demonstrated that a high concentration of phosphate directly stimulates parathyroid hormone (PTH) secretion. High serum levels of phosphate are usually observed in patients with end-stage renal disease. The aim of the present study was to evaluate whether serum phosphate concentration had an acute effect on PTH secretion in hemodialysis patients. The levels of serum phosphate were manipulated during the hemodialysis session by using a phosphate free dialysate or a dialysate with a high content of phosphate.
Methods
Ten stable hemodialysis patients with PTH values above 300 pg/ml were included in the study. A PTH-calcium curve was obtained during both high phosphate and phosphate free hemodialysis.
Results
The serum phosphate concentration remained high (2.17 
0.18 mM) throughout the high phosphate hemodialysis and decreased progressively to normal levels (1.02 0.06 mM) during the phosphate free hemodialysis. The serum PTH levels at maximal inhibition by hypercalcemia (minimal PTH) were greater during the high phosphate than the phosphate free hemodialysis (413 79 vs. 318 76 pg/ml, P < 0.003). In all patients the values of minimum PTH were greater during the high phosphorus than the phosphorus free hemodialysis. The values of maximally stimulated PTH during hypocalcemia and the set point of the PTH-calcium curve were similar during the high phosphate and the phosphate free hemodialysis.
Conclusion
The maintenance of high serum phosphorus levels during hemodialysis prevented, in part, the inhibition of PTH secretion by calcium, which strongly suggests that in hemodialysis patients high serum phosphate contributes directly to the elevation of PTH levels despite normal or high serum calcium concentration.
Keywords:
phosphorus, PTH, hemodialysis, calcium, secondary hyperparathyroidism
