Kinetics of serum parathyroid hormone during and after thyroid surgery

Background: Hypocalcaemia after thyroidectomy is thought to result from surgical damage to the parathyroid glands. This study analysed postoperative outcomes related to perioperative parathyroid hormone (PTH) levels. Methods: Some 402 consecutive patients undergoing thyroid surgery were studied prospectively to monitor perioperative changes in serum PTH and Ca2+ levels, and clinical symptoms of hypocalcaemia. Results: Transient symptomatic hypocalcaemia and persistent hypoparathyroidism occurred in 61 (15 per cent) and six (1.5 per cent) of 402 patients respectively. The intraoperative decline in PTH was 20.2 per cent; the trough (63.8 per cent of preoperative value) was reached 3 h after surgery. Before surgery, PTH levels were correlated inversely with scrum Ca2+ concentration. The correlation remained Positive from 3 h after surgery until postoperative day 14. Thus, PTH secretion was reduced, but remained sufficient to prevent symptomatic hypocalcaemia in most patients. A low serum PTH level was predictive of persistent hypoparathyroidism (sensitivity and negative predictive value 100 per cent, but poor specificity of 54.1 percent). Conclusion: Thyroid surgery, impairs hormone secretion by the parathyroid glands resulting in postoperative latent parathyroid insufficiency. Normal PTH levels 3 h after surgery and a normal serum calcium level on the first postoperative day rule out persistent hypoparathyroidism.