Disadvantages of QPTH and Criterion

The disadvantages of QPTH and the criterion are as follows:

1. QPTH cannot guarantee operative success.

QPTH predicts, but does not prevent, operative failure in patients whose offending gland(s) could not be found by localization studies, differential jugular venous sampling, and careful bilateral neck exploration performed by an experienced surgeon. In addition, it cannot prevent operative failure due to misdiagnosis.

2. QPTH accuracy is criterion and protocol dependent.

If the surgeon is not aware of the possible mistakes and the need for a strict protocol of blood collection and interpretation of the changing hormone values during the procedure, the accuracy of QPTH will decrease considerably. There are several different protocols and criteria to evaluate intraoperative PTH levels. Some studies used criteria that require a drop in the PTH level of 60% or 70%, 10 or 15 minutes after gland resection, to predict operative success.1,40 Others required a drop in the PTH level and its return to the published normal range, or a value below the preincision level, to predict cure.4,17,19,29,35 The different criteria used for evaluating hormone dynamics have different sensitivities and specificities in predicting operative outcome. For instance, in an attempt to not overlook any patients with MGD (QPTH false positive), some require a greater percentage drop in the PTH level at 10 minutes to predict a postoperative return to eucalcemia. Such a change in the criterion leads to an increased number of patients that will not have a sufficient hormone drop in 10 minutes even though they had complete resections of all hypersecreting glands (QPTH false negative). This alteration increases the specificity of this surgical adjunct but decreases its sensitivity, making the use of intraoperative assay less beneficial.27

3. The assay is technician dependent.

This surgical adjunct is dependent on the expertise of the technician in performing the test, handling the blood, and running the assay itself as a functioning system. Plasma pipetting and blood dilutions with a high coefficient variation of the samples, inability to solve system problems (antibodies, washer system and luminometer breakdowns), and delay in sample drawing are all factors that are dependent on good technical skills. The usefulness of QPTH will improve as the assay becomes more automated.

4. The cost of QPTH is high.

This surgical adjunct is expensive. The benefits of QPTH, however, compensate for its cost by allowing a shorter operative time, decreasing the need for frozen section histopathology and eliminating an overnight hospital stay. In an attempt to make QPTH more affordable, some hospitals locate this surgical adjunct at the central laboratory where the system can be used for other purposes without dislocating a technician to the operative room. This limits the use of intraoperative hormone dynamics since the assay turnaround time is prolonged. If the number of samples obtained during parathyroidectomy is reduced to decrease costs (e.g., if the pre-excision sample is omitted from the protocol), the accuracy of the assay will decrease.

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