Multivariate regression analysis showed that negative 99mTcO4- thyroid imaging (95% CI: 1.095 - 8.754, P = 0.033), pre-RAI serum calcium < 2.27 mmol/L (95% CI: 3.092 - 14.466, P < 0.001), and pre-RAI PTH < 4.18 pmol/L (95% CI: 1.067 - 4.335, P = 0.032) were risk factors for hypocalcemia at five days post-RAI. This evidence concerns the gene PTH and Hypocalcemia.