EVIDENCE FOR ABNORMAL CALCIUM HOMEOSTASIS IN PATIENTS WITH ADYNAMIC BONE-DISEASE

To investigate whether the derangements in calcium kinetics in patient s with renal osteodystrophy are similar in the various histologic form s of this metabolic bone disease, 43 patients on chronic maintenance d ialysis underwent calcium kinetic studies using the double isotope tec hnique, iliac crest bone biopsies for mineralized bone histology and h istomorphometry and determinations of serum indices of calcium and bon e metabolism. Intestinal calcium absorption was not different among th e three histologic groups. However, women exhibited lower calcium abso rption in each histologic form (P < 0.01). Patients with predominant h yperparathyroid bone disease showed plasma calcium efflux, calcium acc retion rate and calcium retention markedly above normal values. Patien ts with low turnover bone disease exhibited a normal or slightly decre ased plasma calcium efflux and calcium accretion rate together with a disproportionately low calcium retention. Patients with mixed uremic o steodystrophy presented with a calcium kinetic profile intermediary to the two other forms. Good relationships existed between plasma calciu m efflux, calcium accretion rate, calcium retention and histomorphomet ric parameters of bone turnover as well as serum levels of parathyroid hormone. However, no serum parameter could indicate with certainty th e underlying bone disease. These findings demonstrate that adynamic bo ne disease does not merely represent an academic finding but is charac terized by a very low bone capacity to buffer calcium and inability to handle an extra calcium load. This is particularly relevant for the d aily care of end-stage renal failure patients presently receiving high er than ever amounts of vitamin D and calcium salts.