THE RELEVANCE OF MINERALIZATION LAG TIME IN THE EVALUATION OF HISTOLOGIC-CHANGES IN RENAL OSTEODYSTROPHY

We examined bone biopsies from 47 patients on chronic hemodialysis, an d analyzed the histomorphometric and biochemical findings and histolog ic quantitation of bone aluminum, looking primarily at mineralization lag time (Mlt) to evaluate its usefulness in categorization of renal o steodystrophy (ROD). The patients were categorized as having either re latively normal Mlt (<35 days, n = 21 patients), moderately prolonged Mlt (35-100 days, n = 13 patients) or markedly prolonged Mlt (>100 day s, n = 13 patients). The group with relatively normal Mlt showed signi ficantly higher C-terminal parathyroid hormone (PTHc) levels (26,141 /- 19,270 vs 7,226 +/- 6,073 and 4,434 +/- 4,000 pg/ml) than the moder ately or markedly prolonged Mlt groups (p <.01) and was associated wit h histologic characteristics of osteitis fibrosa or mild hyperparathyr oidism (BFR/BS range 0.146-0.947 mcm3/mcm2/d). The group with markedly prolonged Mlt included one patient with classic and 11 with adynamic osteomalacia (BFR/BS range 0.009-0.099) and had greater bone aluminum (Al.S/OS 35.3 +/- 26.7% vs 7.2 +/- 9.0%) than the normal Mlt group (p <.01). The group with moderately prolonged Mlt included two patients w ith aplastic bone disease (Mlt 80.0 and 84.6 days, and Al.S/OS 100.0 a nd 72.3%) and 11 patients with features of hyperparathyroidism and ost eomalacia (BFR/BS range 0.068-0.243) with variable but generally inter mediate bone aluminum deposition (Al.S/OS 22.5 +/- 19.9%). Like BFR/BS and other dynamic parameters Mlt correlates with morphologic types of ROD which primarily reflect bone turnover, but it may also suggest va rying degrees of mineralization impairment in a spectrum ranging from high to low turnover types of ROD. Its usefulness in this respect shou ld not be overlooked.