PTH and vitamin D deficiency: However, in univariate analysis of the ΔPTH50− and ΔPTH50+ groups, female gender and N0 stage were statistically significant predictors of postoperative PTH reduction ratio ≥50% (p = 0.027 and 0.047, respectively), but not independent risk factors after adjusted with vitamin D insufficiency in multivariate analysis (p = 0.0282 and 0.104, respectively).