HDCN Article Review/Hyperlink

Pahl M, Aquiles J, Bover J, Rodriguez M, Felsenfeld A

The set point of calcium and the reduction of parathyroid hormone in dialysis patients

Kidney Int (Jan) 49:226-231 1996

In this study, Pahl et al. evaluate the effects of increasing the serum calcium on the set point for PTH secretion in 11 hemodialysis patients. They define the set point as the serum total calcium level (not ionized) at which the maximum PTH level was decreased by 50% during calcium induced PTH suppression/stimulation testing. The patients were randomized to a group where calcium levels were increased by using a dialysate Ca of 3.5 mEq/L and 2 ug IV calcitriol/3X weekly (N=5) or by using a dialysate Ca of 4.0 mEq/L and "more" Ca supplements (N=6). Patients in each group had suppression/stimulation done at baseline, six weeks of treatment, and six weeks post treatment.

Both groups had higher levels of basal Ca and lower maximum stimulated PTH levels after treatment. The basal PTH levels were not different (although when the two groups were combined they decreased with treatment). The set point increased with increasing Ca levels in each group. The authors conclude that the e set point of Ca may not be a reliable indicator of the magnitude of hyperparathyroidism during calcitriol treatment in hemodialysis patients. They suggest that PTH secretion may adapt to the ambient serum Ca concentration.

Comment: A nice study involving a relatively small number of subjects reemphasizing how difficult it is to relate in vivo to in vitro events. James A. Delmez, MD, Washington University at St. Louis, MO