The concept that the PTH-
calcium curve is representative of parathyroid function has been discussed. Comparisons of parathyroid function have been made between normal humans and
hemodialysis patients and also between
hemodialysis patients with different forms of
renal osteodystrophy. From these comparisons, it is apparent that the magnitude of HPT is much greater in patients with
renal failure than in normal humans, and as represented by the ratio of basal to maximal PTH, the parathyroid gland appears to be stimulated at basal serum
calcium levels in
hemodialysis patients. Similarly, based on an analysis of the PTH-
calcium curve, we were able to determine that several differences in parathyroid function were present in
hemodialysis patients with different forms of
renal osteodystrophy. As compared to
hemodialysis patients with LTAABD and aplastic
bone disease, patients with
osteitis fibrosa have a greater magnitude of
hyperparathyroidism, a greater sensitivity of the parathyroid cell (slope), a higher set point of
calcium, and greater PTH stimulation at basal serum
calcium (ratio of basal to maximal PTH).
Calcitriol treatment of
hemodialysis patients with
osteitis fibrosa resulted in a significant decrease in PTH throughout the PTH-
calcium curve and also reduced the sensitivity (slope) of the PTH-
calcium curve. The concept of hysteresis has been discussed as well as the role that the ambient basal serum
calcium concentration may have on the determination of the PTH-
calcium curve. Finally, the effect that successful
renal transplantation has on HPT has been examined. In conclusion, we believe that the PTH-
calcium curve provides a reliable assessment of parathyroid function, and as such, has considerable application for the study of
parathyroid disorders in the clinical setting.