PTH Gradient as a Predictor of Post Thyroidectomy Hypocalcemia

BACKGROUND: Post thyroidectomy hypocalcemia is a common complication. Post thyroidectomy PTH estimation at varying cut offs and time have been used to predict hypocalcemia and aid in early and safe discharge. Single post thyroidectomy PTH values may be spuriously normal or high in a patient that subsequently develops unanticipated low calcium levels. This study aimed to evaluate the percentage change in preoperative and postoperative PTH (Gradient) in predicting post thyroidectomy hypocalcemia. METHODS: Forty-one patients of thyroidectomy had PTH preoperatively, postoperatively one-hour (PTH0) and day 1 (PTH1). PTH gradient was calculated as percentage change in postoperative PTH to preoperative (PTHG0, PTHG1). Hypocalcemia was categorized into mild or severe based on corrected calcium values and presence of clinical signs and/or symptoms of hypocalcemia. RESULTS: Ten (24.3%) and 11 (26.8%) patients had mild and severe hypocalcemia, respectively. PTHG0 and PTHG1 were significantly associated with risk for hypocalcemia (P-0.006 vs P-0.002). Higher PTH0 and PTH1 gradients were significantly associated with risk of hypocalcemia (PTH0 gradient OR-0.006, 95% CI 0.00–0.175, P-0.006; PTH1 gradient OR- 0.008, 95% CI 0.00–0.166, P-0.002). PTH0 gradient was the best predictor of hypocalcemia (AUC 0.855, SE-0.065, 95% CI0.710 to 0.945, P value <0.001) and PTH1 value was a better predictor of severe/clinical hypocalcemia (AUC 0.844, SE-0.072, 95% CI 0.697 to 0.938, P- value-0.001). Based on ROC, cutoffs of PTH0 gradient and PTH1 gradient for predicting hypocalcemia and severe/clinical hypocalcemia were taken as 60% and 75%, respectively (sensitivity 70%, specificity 90.5% for hypocalcemia; sensitivity 65%, specificity 90.9% for severe hypocalcemia). CONCLUSION: PTH gradient may be a better predictor of hypocalcemia and PTH1 gradient of >75% correlates with high risk of severe/clinical post thyroidectomy hypocalcemia.