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, and analyzed the histomorphometric and biochemical findings and histologic quantitation of bone aluminium, looking primarily at mineralization lag time (Mlt) to evaluate its usefulness in categorization of renal osteodystrophy (ROD). The patients were categorized as having either relatively normal Mlt (< 35 days, n = 21 patients), moderately prolonged Mlt (35-100 days, n = 13 patients) or markedly prolonged Mlt (> 100 days, n = 13 patients). The group with relatively normal Mlt showed significantly 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 moderately or markedly prolonged Mlt groups (p < .01) and was associated with histologic characteristics of osteitis fibrosa or mild hyperparathyroidism (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 with aplastic bone disease (Mlt 80.0 and 84.6 days, and Al.S/OS 100.0 and 72.3%) and 11 patients with features of hyperparathyroidism and osteomalacia (BFR/BS range 0.068-0.243) with variable but generally intermediate 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 varying degrees of mineralization impairment in a spectrum ranging from high to low turnover types of ROD. Its usefulness in this respect should not be overlooked.