Kinetics of serum parathyroid hormone during and after thyroid surgery

Abstract

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. 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. 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 serum 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 per cent). 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.