Background: To investigate the impact of the percent change of postoperative parathormone (PoPTH) level from baseline value (∆PTH) on the rate of hypocalcemia after total thyroidectomy. Methods: Assays of serum PTH and calcium (Ca) were performed preoperatively and at 24 hours postoperatively in 222 consecutive patients who underwent total thyroidectomy. Postoperative hypocalcemia was defined as serum calcium level corrected for albumin concentration (cCa) <8.5mg/dl. Patients with postoperative hypocalcemia were classified as group1 (n=100) and those with normal Ca levels as group 2 (n=122). The PoPTH levels and ∆PTH were compared between the two groups. ROC analysis was performed to determine the cut off values for PoPTH and ∆PTH. Results: The mean PoPTH level was significantly lower in group 1 compared to group 2 (18.6±15.3 pg/ml vs 32.3±15.6 pg/ml, respectively; P<0.0001). PoPTH values were within normal range in 54% of the patients with hypocalcemia and 35% of those with symptomatic hypocalcemia. PoPTH <28pg/ml or ∆PTH >45 were significantly associated with increased risk of post-thyroidectomy hypocalcemia (P=0.0001). A ∆PTH >70% ,PoPTH ≤ 15.5pg/ml and postoperative serum cCa concentrations<8.0mg/dl significantly predicted symptomatic hypocalcemia(P=0.009;P=0.006;andP=0.0001;respevtively).The sensitivities of ∆PTH,PoPTH level and postoperative serum cCa concentration to predict symptomatic hypocalcemia were 67%,64% and100, respectively. Conclusion: Although, PTH decline significantly correlate with symptomatic hypocalcemia, a considerable number of patients may experience hypocalcemic symptoms in spite of normal PoPTH levels. Analysis of serum Ca concentrations at 24 hours postoperatively help to achieve a more precise prediction of patients who bear a high risk for developing hypocalcemic symptoms.

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