Parathyroid hormone response to hypocalcemia in hemodialysis patients with osteomalacia

Abstract

The parathyroid hormone response to hypocalcemia was investigated in hemodialysis patients with osteomalacia and compared to those with osteitis fibrosa. Hypocalcemia was induced during hemodialysis by employing a dialysate devoid of calcium. Patients with osteomalacia had a blunted maximum amino terminal parathyroid hormone response (± SD) (0.39 ± 0.33 vs. 0.87 ± 0.53 ng/ml, P < 0.05) and maximum carboxy terminal parathyroid hormone response (± SD) (0.36 ± 0.20 vs. 0.84 ± 0.47, P < 0.02) to hypocalcemia. The decline in plasma calcium was greater in patients with osteomalacia at 90 (P < 0.05), 120 (P < 0.01), and 150 min (P < 0.01). In osteomalacia patients the surface density of histologically detectable trabecular bone aluminum correlated directly with the percent relative osteoid volume (P < 0.005) and inversely with the maximum amino terminal parathyroid hormone response to hypocalcemia (P < 0.025). These results suggest that hemodialysis patients with osteomalacia have diminished secretion of parathyroid hormone and a decreased ability to restore plasma calcium homeostasis during hypocalcemia.