Short-term effects of parathyroidectomy on plasma biochemistry in chronic uremia

Abstract

Parathyroidectomy (PTx) is indicated in hemodialysis (HD) patients who have severe osteitis fibrosa unresponsive to vitamin D therapy or in whom the latter treatment is contraindicated. Immediately after PTx, plasma immunoreactive parathyroid hormone, calcium and phosphorus concentrations decline abruptly. However, little is known in such patients about the short-term effects of PTx on plasma alkaline phosphatase (AP) activity and plasma aluminum (Al) levels. The present, preliminary study was performed to determine such parameters in 37 HD patients, and to correlate them with data of bone histology. Mean plasma AP activity started to increase after PTx from day 4 onwards. Thus, AP values significantly higher than pre-PTx values were observed at day 7 and 14 (415 ± 54 vs. 619 ± 77 and 749 ± 83 IU/liter, means ± SEM; N = 37; P < 0.05 and 0.001, respectively). This increase in the absence of changes in liver function, was mainly due to the bone-specific iso-AP. Moreover, the degree of increase in plasma AP activity was higher in the subgroup with negative (group I, 21 patients) than in that with positive bone Al staining (group II, 16 patients). However, plasma osteocalcin (BGP) did not change after PTx (N = 8). Basal plasma Al levels were significantly higher in group II both before and two weeks after surgery. The mean increase of plasma Al level after a deferoxamine (DFO) infusion test was higher in group II than in group I both before (10.8 ± 1.6, vs. 4.6 ± 0.8 μmol/liter, P < 0.001) and after PTx (6.5 ± 1.5, vs. 2.6 ± 0.6 μmol/liter, P < 0.01). Moreover, the mean increase of plasma Al after DFO was significantly higher before than after PTx in both groups. In conclusion, this study in uremic patients shows the occurrence, immediately after PTx, of both a consistent increase in plasma AP activity (probably reflecting flare up of osteoblastic activity) and a significant decrease of tissue Al mobilization under DFO chelation. Even though hypotheses have been formulated to explain these findings, further studies are needed to understand their relation with skeletal changes in response to parathyroid gland removal.