PTH and Hypocalcemia: In this latter study, a decline in serum intact PTH levels by more than 60%, in conjunction with a decline in serum calcium levels of more than 10%, 5 to 6 hours postoperatively had the best results (a sensitivity, specificity, and positive predictive value of 100%) for identifying patients at high risk of developing symptomatic hypocalcemia after total thyroidectomy [3].