Calcium balance in uremia: longitudinal study of long-term survivors

Twelve male patients surviving uremia of 9-15 years duration were studied sequentially over a mean period of 9.2 years. Radiographs, bone biopsies, bone mineral mass (BMM) measured by photon absorptiometry, and total body calcium (TBC) determined by in vivo neutron activation analysis (NAA) were used. Pathologic fractures correlated with TBC corrected for height: 4 of 5 patients without fractures had TBC above 80% predicted, whereas 5 of 7 patients with fractures fell below this value. Unlike previous studies, negative calcium balance was seen in 3 patients with prolonged hyperparathyroidism. Though soft tissue calcification occurred in 6 patients, only 1 with massive shoulder calcification had an increase in TBC; this drawback of NAA has been previously overemphasized. Moreover, radial BMM also increased in 2 patients due to soft tissue calcification. When viewed at a single point in time, nearly all patients fell within the wide normal limits of BMM vs TBC. However, 6 patients with variable bone histology studied sequentially over a mean of 8.5 years showed significant preferential loss of radial bone mass compared to TBC. Aluminium retention did not influence calcium balance in these subjects.