BONE-DISEASE IN PREDIALYSIS, HEMODIALYSIS, AND CAPD PATIENTS - EVIDENCE OF A BETTER BONE RESPONSE TO PTH

The spectrum of bone disease in predialysis and dialysis patients has changed during the last decade. The incidence of aplastic bone disease has increased and this can not be attributed to bone aluminum deposition; moreover, low bone cellular activity is present despite a moderate elevation in PTH levels. This study compares PTH levels and types of bone disease in both predialysis and dialysis patients from the same geographical area. We prospectively studied 119 unselected end-stage renal disease patients: 38 were immediately predialysis (PreD), 49 on hemodialysis (HD), and 32 on CAPD. A bone biopsy was performed in all patients. Aplastic bone disease with < 5% bone surface aluminum was a common finding (48%, 32%, and 48%, in PreD, HD, and CAPD, respectively). In all groups, an intact PTH level below 120 pg/ml was highly predictive of low bone turnover. Conversely, a PTH level above 450 pg/ml was always associated with histologic features of hyperparathyroid bone disease. Among the bone histomorphometric parameters, osteoblast surface showed the best correlation with intact PTH in each group, and the slope of the regression line for this correlation was significantly steeper in HD and CAPD than PreD patients. Thus, the range of PTH (95% confidence limit bands) needed to obtain a normal osteoblast surface of 1.5% was greater in preD than in HD and CAPD patients (300 to 500 vs. 75 to 260 pg/ml, respectively). In all groups some degree of marrow fibrosis was observed when PTH levels were greater than 250 pg/ml. Thus, PTH levels of 120 to 250 pg/ml (2 to 4 times the upper normal limit) were required to avoid low bone turnover and hyperparathyroid bone disease in patients receiving maintenance dialysis. By contrast, in preD patients, a PTH range of 300 to 500 pg/ml was required to maintain a normal osteoblast surface; however, this range of PTH levels was also associated with a mild degree of marrow fibrosis. If mild marrow fibrosis (< 0.5%) was admitted, the corresponding PTH range was 300 to 375 pg/ml. In conclusion, aplastic bone disease without significant bone surface aluminum was a common finding in our predialysis, hemodialysis, and CAPD patients. Maintenance dialysis improved the bone response to PTH. Finally, the results of our study help define a range of intact PTH levels that would be desirable in order to avoid both aplastic bone disease and significant hyperparathyroid bone disease.