COMPARISON OF BONE-FORMATION RATES MEASURED BY RADIOCALCIUM KINETICS AND DOUBLE-TETRACYCLINE LABELING IN MAINTENANCE DIALYSIS PATIENTS

We report 23 prospective studies on 18 maintenance dialysis patients i n whom we measured skeletal mineralization rate (m) using Ca-47, analy zed by the expanding pool model, and compared it with the histologic b one formation rate (bfr), volume referent, estimated on tetracycline-l abeled iliac crest bone. The patients showed a spectrum of bone diseas e types including adynamic bone, aluminum-related osteomalacia, and va rious degrees of secondary hyperparathyroidism. The mean width between double labels, on which mineral apposition rate depended, was estimat ed using a simple formula relating area to perimeter for each feature enclosed by the labels. Values for m ranged from 0 to 155 mmol calcium per day and for bfr from 0 to 124% per year. There was close correlat ion between m and bfr (r = 0.976), serum alkaline phosphatase (r = 0.9 68), and serum immunological parathyroid hormone (iPTH) (r = 0.868). W hen the volumetric bfr was converted to mass units and applied to the whole skeleton, using literature values for mineral density and cortic al and trabecular mass, there was close agreement between the histolog ic and isotopic estimates of m (r = 0.959). The results validate the t wo methods and suggest they are interchangeable. However, use of a rig orous method to determine bfr appears to be essential.