The role of parathyroid hormone monitoring after total thyroidectomy in predicting post-thyroidectomy related hypocalcaemia
Evangelos Athanassiou, Gregory Christodoulidis, Constantinos Hatzitheofilou, Constantinos Tepetes, Demetrios Zacharoulis, George Tzovaras & Manthos Euthymiou
Objective: Clinically apparent hypocalcaemia following total thyroidectomy occurs in 2025% of patients subjected to total thyroidectomy, in 2-4% of these patients the hypocalcaemia is permanent. Treatment by per-os or iv administration of calcium supplements and vitamin D is suggested when the serum calcium concentration falls bellow a critical level, either before or whenever the patients develop clinical symptoms of tetany. The purpose of this study is to evaluate the parathyroid hormone (PTH) serum levels, measured 6, 12, and 24 hours postoperatively, as predictors of hypocalcaemic symptoms in patients undergoing total thyroidectomy.
Materials and methods: In a period of 2 years (20042006) 108 patients were subjected to total thyroidectomy for benign or malignant thyroid pathology. Serum PTH, ionized serum calcium, and serum phosphorus levels were measured prior to surgery, 6, 12, and 24 hours postoperatively.
Results: In thirty-one out of 108 patients postoperative hypocalcaemia was observed (28,7%). In four of the 31 patients permanent symptomatic hypocalcaemia occurred, requiring vitamin D and calcium supplements indefinitely (3.7%). Tetany in 22/31 patients with PTH levels lower than 8pg/ml (normal range 8 pg/ml75 pg/ml). These patients required vitamin D and calcium supplements for a few weeks or months (transient hypocalcaemia). Although 5/31 patients with clinical symptoms of hypocalcaemia (tetany) had the PTH levels recorded postoperatively within the normal range, an abrupt decline of serum PTH of more than 50% of the initial preoperative value was observed. These patients were also treated with vitamin D and calcium supplements for a few weeks postoperatively until the normal function of the parathyroid glands recovered (transient hypocalcaemia). In 77 out of 108 patients with normal calcium, phosphorus and PTH levels no symptoms of hypocalcaemia were noticed.
Conclusion: Following total thyroidectomy, an abrupt decrease in PTH serum levels either within or below the lower value of the normal range, a few hours postoperatively, serves as a reliable predictor of the development of clinically significant hypocalcaemia. Further studies are required however for validation of post-op PTH levels assay, in identification of a group of operated patients requiring prompt early therapy before tetany occurs.