Background
Primary hyperparathyroidism is a common condition caused by single or multiple parathyroid lesions; it is rare below the age of 50 years but rises thereafter, particularly in women; surgery offers the only definitive treatment.
The aim of parathyroidectomy is to establish normocalcaemia trying to avoid complications such as persistent or recurrent hyperparathyroidism, postoperative transient or persistent hypoparathyroidism and recurrent laryngeal nerve injury.
Primary hyperparathyroidism has traditionally been managed by bilateral neck exploration and identification of the four parathyroid glands with a success rate of more than 95% when performed by experienced endocrine surgeons.
The traditional surgical approach with the visualization of all parathyroid glands and the resection of apparently enlarged glands has been increasingly replaced by minimally invasive (unilateral) surgical procedures, supported by preoperative imaging and rapid intraoperative parathyroid hormone (PTH) assay measurement.
However, 5% to 20% of patients with primary hyperparathyroidism have multiglandular disease and require bilateral neck exploration; in such cases, imaging studies can be misleading.
PTH monitoring during the surgical procedure can confirm the removal of all hyperfunctioning parathyroid tissue, as the half-life of PTH is approximately 5 min. An insufficient decrease in PTH indicates persisting primary hyperparathyroidism, leading to more extended (bilateral) exploration within the same session.
The commonly applied Irvin criterion (rapid intra-operative PTH assay drop ≥ 50% from the highest value of either pre-incision or pre-excision level at 10 min after gland excision) is reported to correctly predict post-operative calcium levels in 96–98% of patients and incorrectly in only 2–4%. Some authors suggest to fulfill various percentage drop versus pre-incision or pre-excision PTH, 5–10 min after resection of the suspected parathyroid adenoma, or to reach a final PTH concentration within the normal range.
However, the PTH baseline reference concentration is markedly influenced by surgical manipulations during preparation of the affected glands, interindividual variability of the PTH half-life and modifications in the physiological state of the patient during surgery (such as changes of clearing rate or expanded volume of intra-operative infusions).
Some authors have reported error rates of as much as 16% due to false-negative and false-positive results.
The aim of this study was to evaluate the role of the measurement of intraoperative PTH 20 minutes after surgery.