Significant role of 1,25-dihydroxyvitamin D on serum calcium levels after total thyroidectomy: a prospective cohort study

IntroductionAlthough active vitamin D (VD) has been used both preoperatively and postoperatively to prevent hypocalcemia risk in patients undergoing total thyroidectomy, the role of 1,25-dihydroxyvitamin D (1,25(OH)2D) has not been examined. This study comprehensively investigated the effects of 1,25(OH)2D on calcium (Ca) concentrations after total thyroidectomy.MethodsSerum Ca, parathyroid hormone (PTH), and 1,25(OH)2D levels were measured in 82 patients with thyroid disease before and after surgery.ResultsSerum Ca, PTH, and 1,25(OH)2D levels decreased significantly on the morning of the first postoperative day. Notably, the decrease in 1,25(OH)2D concentration was significantly lower than that of PTH concentration (10.5 ± 33.4% vs. 52.1 ± 30.1%, p<0.0001), with 28% of patients showing increases in 1,25(OH)2D. The only factor predicting a postoperative 1,25(OH)2D decrease was a high preoperative 1,25(OH)2D concentration. Postoperative 1,25(OH)2D concentrations, as well as the magnitude and rate of decrease from preoperative levels, showed strong positive correlations with preoperative 1,25(OH)2D concentrations (p<0.0001 for all three variables) but not with PTH concentrations. These findings suggest that 1,25(OH)2D concentrations after thyroidectomy were more strongly dependent on preoperative concentrations than on the effect of PTH decrease and were relatively preserved, possibly preventing sudden severe postoperative hypocalcemia. A high 1,25(OH)2D level was the most important preoperative factor for hypocalcemia (<2 mmol/L; p<0.05) on the first postoperative day; however, only PTH decrease was statistically significant (p<0.001) when intraoperative factors were added. In the PTH >10 pg/mL group, the decrease in 1,25(OH)2D levels was significantly associated with postoperative hypocalcemia (p<0.05). Similarly, in the PTH levels >15 pg/mL group, a decrease in 1,25(OH)2D concentration was a significant factor, and the amount of PTH decrease was no longer significant.Conclusion1,25(OH)2D plays an important role in preventing sudden, severe hypocalcemia due to decreased PTH levels after total thyroidectomy, whereas high preoperative 1,25(OH)2D levels are a significant risk factor for postoperative hypocalcemia. Optimizing preoperative protocols to adjust Ca, PTH, and 1,25(OH)2D levels to improve the management of patients undergoing total thyroidectomy and to prevent extreme intraoperative PTH decreases may reduce the risk of hypocalcemia

High Frequency of Deletions at the Hypoxanthine-guanine Phosphoribosyltransferase Locus in an Ataxia-telangiectasia Lymphoblastoid Cell Line Irradiated with gamma-Rays

The molecular nature of gamma-ray-induced mutations at the hypoxanthine-guanine phosphoribosyltransferase (HPRT) locus in an ataxia-telangiectasia (A-T) lymphoblastoid cell line was investigated. Twelve of 15 gamma-ray-induced HPRT-deficient mutants showed deletions. Eight of them had lost the entire HPRT gene, one showed a 1.9-kb deletion, and three had deletions of about 40 - 150 base pairs. Of the eight mutants that lost the entire gene, five had also lost both DXS79 and DXS86, flanking markers of the HPRT locus. The spectrum of mutations induced by gamma-irradiation in the A-T cells showed a high frequency of deletions in comparison with that in a control cell line, WIL2-NS. Sequence analysis of breakpoint junctions in four mutants revealed that three of them had junctions between short identical sequences at each breakpoint, leaving one copy at the junction. These results suggest that non-homologous end-joining is the major mechanism for deletion formation in A-T cells