Limitations of the Established Criterion

It is important to understand that QPTH only measures PTH levels at any given time during parathyroidectomy. Most published limitations of the intraoperative assay are related to the protocol and criteria used to interpret the intraoperative hormone values and not to the assay itself. The use of different protocols and criteria in interpreting the hormone levels has led to reports that differ in degrees of accuracy.17'19'23'27'29'35"43

1. QPTH and criterion do not predict the size of the remaining normally secreting parathyroid glands.

Some surgeons using QPTH during bilateral neck explorations have published the finding of a second enlarged, but not hypersecreting, gland after successful resection of a single adenoma confirmed by the drop in hormone levels. Because these enlarged, normally functioning glands are interpreted as "second adenomas" and are excised, the QPTH results were reported as false positive because eucalcemia is achieved.36-37-39'41'43 The criterion used in our series does not predict the size of the remaining normally functioning glands. These glands were not hypersecreting either at the time of the surgery or found to be responsible for hypercalcemia during the postoperative period, which averaged 3 years.18 This emphasizes that abnormal secretion is not necessarily associated with parathyroid gland size.44-45 This can also be supported by the fact that when parathyroid resection is guided by hormone secretion, 6% fewer glands are excised with a 98% success rate, when compared with gland resection guided by the surgeon's judgment of gland size. Therefore, we can conclude that those enlarged glands left in situ were not hyperfunctioning.18

2. QPTH and criterion do not predict PTH levels in postoperative eucalcemic patients.

Some authors have pointed out that the use of QPTH in parathyroidectomy, with this described criterion, fails to predict high PTH levels in postoperative eucalcemic patients. It is known that despite the operative approach used, PTH levels are found to be elevated in 8% to 17% of eucalcemic patients following successful parathyroidectomy. Many of these patients return to normal PTH levels months later.46"49 Carty,4 Bergenfelz,46 and their associates have suggested that these high PTH levels are compensatory, with parathyroid glands responding to a deficit in total body calcium. We observed no difference in intraoperative hormone dynamics found in eucalcemic patients presenting with normal or high postoperative PTH levels.

3. QPTH and criterion do not predict late recurrence.

No difference was found in the operative hormone dynamics between long-term postoperative eucalcemic patients and those who developed recurrent hypercalcemia.

4. QPTH and criterion do not identify the secretion of the first glands resected in a MGD case.

If, after resection of an enlarged parathyroid gland, the hormone level does not drop sufficiently and a second gland is found and resected with a sufficient hormone drop, it is not possible to evaluate the parathyroid hormone secretion of the first resected gland. QPTH does not differentiate this gland from an enlarged normally functioning parathyroid, because the hormone level remained high after its removal.

5. The described criterion does not accurately predict the postoperative outcome in patients with secondary hyperparathyroidism (HPT) and multiple endocrine neoplasia (MEN).

The outcome of patients with secondary HPT and MEN may be predicted by a different criterion, but a drop of

50% in the hormone level from the highest preincision or pre-excision level, as measured by the cunrent PTH assays, does not accurately predict outcome in patients with these diseases.28,30,43,50'51 One must not combine QPTH results in secondary, tertiary HPT, and MEN patients in an attempt to evaluate the usefulness of QPTH and the described criterion in the treatment of SPHPT, since the outcome and etiologies are different.43

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