Primary hyperparathyroidism: biochemical features and intraoperative monitoring of intact PTH during surgery.

Objectives: To evaluate the efficacy of rapid intraoperative assay of intact parathormone (iPTH) in patients with primary hyperparathyroidism. Methods: In 42 patients with primary hyperparathyroidism, 32 with single adenoma and 10 with multiglandular disease, preoperative serum calcium (Ca), alkaline phosphatase (AP) and iPTH were evaluated. All these biochemical indexes presented lognormal distributions without significant differences between the two subgroups. Natural logarithm (ln) of serum Ca (mg/dl): mean 2.457, range 2.231 - 2.683 (actual range, after antitrasformation, 9.31 - 14.6); ln serum AP (U/l): mean 5.865, range 4.901 - 6.828 (actual range 134 - 923); ln serum iPTH (pg/ml): mean 5.293, range 3.603 - 6.983 (actual range 36.7 - 1078). Lognormal distribution was supposed for tumour size too: mean (ln) 7.548 mm3, range 4.513 - 10.582 (actual range 91.2 - 39437). Since iPTH has a half-life of a few minutes, plasma samples taken at the induction of anaestesia, and 10, 15, 20 and 30 minutes after the abnormal gland(s) excisions were monitored intraoperatively to confirm significant changes in circulating hormone. Each sample was assayed with a rapid IRMA and the longer standard method. Results Multiple regression demonstrated positive partial correlations between preoperative serum iPTH and serum Ca (r = .347, p < .05), and serum AP (r=.480, p < .002), and tumour size (r = .473, p < .005). There was no partial correlation between tumour size and serum Ca or AP levels. A modified IRMA for intraoperative iPTH allowed to obtain results in about 40 minutes from gland(s) excision. The correlation (r) between the results of the modified and the standard method was .988, p < .000001. At 15 minutes after the removal of the adenoma the mean value of iPTH levels was 17.05% of basal value (SE 2.11%). In patients with hyperplasia the same decline figure was obtained after the last excision. Conclusion: The exclusive significant correlation between serum iPTHT and tumour size confirms that (a) the measurement of iPTH in patients with primary hyperparathyrodism can predict tumour size and (b) intraoperative monitoring of iPTH values can be used to monitor the success of surgery.