LOUISVILLE, KY. — Patients who have undergone surgery for primary hyperparathyroidism do not benefit from routine measures of parathyroid hormone unless they have elevated calcium levels, according to a review presented by Dr. Tina Wei-Fang Yen at the annual meeting of the Central Surgical Association.
“We propose that calcium levels be obtained postoperatively at 1–2 weeks. If normal, they should be repeated at 6 months and then yearly. If the calcium level is elevated at any time point, we recommend checking the [parathyroid hormone] level,” said Dr. Yen.
Her advice is based on the findings of a review that found routine postoperative parathyroid hormone (PTH) testing of questionable benefit, even among the 20%–40% of patients with elevated PTH levels and normal serum calcium levels after curative parathyroidectomy. Furthermore, this additional testing adds cost and can make patients anxious, commented Dr. Yen of the general surgery department at the Medical College of Wisconsin, Milwaukee.
Dr. Yen and her associates compared the utility of postoperative and intraoperative PTH testing with that of intraoperative PTH testing alone.
The investigators used a prospective database of 328 consecutive patients who had PTH levels measured during and after 330 parathyroidectomies performed in 1999–2004.
In the study, the intraoperative PTH testing criteria used to conclude each operation included a measurement of the PTH level at 10 minutes after resection of the last parathyroid gland. This PTH level was at least 50% lower than the baseline value and was in the normal range of the intraoperative PTH assay.
Patients' calcium levels were measured at 1 week, 3 months, and 6 or more months after the operation. Normocalcemia at 6 or more months follow-up was considered to be a cure, Dr. Yen said.
In surgeries that met the intraoperative PTH testing criteria, the cure rate was 98.2%, which is similar to values reported in the literature, Dr. Yen said. A normal postoperative PTH level predicted cure, with a positive predictive value of 97.1% at 1 week, 97.3% at 3 months, and 96.5% at 6 months.
However, operative failure was not predicted with much success by failure to meet the intraoperative PTH testing criteria or by elevated PTH levels after surgery. Only 23.2% of the cases that failed to meet intraoperative PTH testing criteria proved to be actual failures. Furthermore, an elevated postoperative PTH level predicted operative failure in 13.7% at 1 week, in 14.3% at 3 months, and in 14% at 6 months. Most patients with elevated postoperative PTH levels were normocalcemic at follow-up of 6 months or longer, Dr. Yen said.
The percentage of cured patients who had an elevated postoperative PTH level ranged from 16% at 1 week after surgery to 25% at 6 months after surgery. Among the 315 patients who were cured, postoperative PTH measurements followed no distinct trend, regardless of whether the postoperative PTH level was initially normal or elevated at 1 week after surgery. Postoperative PTH values also fluctuated between elevated and normal values among the 15 patients whose operations failed.
“Although we do not have postoperative PTH values for every patient at every time point, our data demonstrate that postoperative PTH values fluctuate over time and do not predict failure well,” Dr. Yen said.