Pahl M, Aquiles J, Bover J, Rodriguez M, Felsenfeld A
The set point of calcium and the reduction of parathyroid
hormone in dialysis patients
(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
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
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
Comment: A nice study involving a relatively small number of
reemphasizing how difficult it is to relate in vivo to in vitro events.
James A. Delmez, MD, Washington
University at St. Louis, MO