Established Criterion for Evaluation of Intraoperative Hormone Levels

The QPTH criterion to predict operative success (normal or low calcium levels for at least 6 months after parathyroidectomy) used in our institution is a drop in the PTH level of 50% or more from the highest level, either preincision or pre-excision, 10 minutes after complete resection of all hyperfunctioning tissue. This criterion was studied and selected before 1993 when the assay was used with previously standard bilateral neck explorations and has proven to be effective through prospective use in patients with SPHPT since.23,18'20"22'27 If there is not a sufficient drop in the hormone level at the 10-minute interval following the excision of a suspected gland, further cervical exploration is mandatory in an attempt to find and resect the remaining hyperfunctioning parathyroid tissue. Figure 52-1 graphically pictures the intraoperative PTH results obtained in a patient with excision of a single hyperfunctioning parathyroid gland. The 92% drop in the PTH level 10 minutes after excision of a single tumor confirms that no other hypersecreting parathyroid glands are present and predicts postoperative eucal-cemia. Further neck exploration in an attempt to visualize and/or biopsy the remaining normally secreting parathyroid glands is not necessary. Figure 52-2 shows the PTH levels measured by QPTH in a patient with two hyperfunctioning parathyroid glands. After excision of an enlarged parathyroid gland in the right superior position, the hormone level did not decrease 50% from the pre-excision level, signifying that further exploration was necessary. This led to the

Enlarged right inferior parathyroid gland excision

PTH pg/mL

PTH pg/mL

Parathyroid adenoma

Pre-incision Pre-excision

5min 10min

FIGURE 52-1. Timed measurements of intraoperative hormone levels before and following excision of a single hypersecreting parathyroid gland. Intact parathyroid hormone (PTH) levels are expressed in picograms per milliliter. The 10-minute postexcision sample represents a 92% drop in hormone level from the highest pre-excision value. At 10 minutes following the excision of all hypersecreting glands, a drop in the hormone level greater than 50% from the highest peak before tumor excision meets the criterion for predicting postoperative normal or low serum calcium levels.

Parathyroid adenoma

Pre-incision Pre-excision

5min 10min

Timed operative blood samples

FIGURE 52-1. Timed measurements of intraoperative hormone levels before and following excision of a single hypersecreting parathyroid gland. Intact parathyroid hormone (PTH) levels are expressed in picograms per milliliter. The 10-minute postexcision sample represents a 92% drop in hormone level from the highest pre-excision value. At 10 minutes following the excision of all hypersecreting glands, a drop in the hormone level greater than 50% from the highest peak before tumor excision meets the criterion for predicting postoperative normal or low serum calcium levels.

Enlarged right inferior parathyroid gland excision

PTH pg/mL

Enlarged right superior parathyroid gland excision

Pre- Pre- 5 min incision excision

10 min Pre- 5 min excision 2

PTH pg/mL

Enlarged right superior parathyroid gland excision

Pre- Pre- 5 min incision excision

10 min Pre- 5 min excision 2

10 min

Timed operative blood samples

FIGURE 52-2. Hormone levels obtained during parathyroidectomy in a patient with multiglandular disease. A drop of 30% after excision of the right superior parathyroid resection did not predict a return to eucalcemia. Further exploration resulted in excision of a hypersecreting gland in the right inferior parathyroid gland with a decrease of 58% in the hormone level predicting operative success. PTH = intact parathyroid hormone.

discovery and excision of the second hyperfunctioning parathyroid gland, in the right inferior position, resulting in a drop in the PTH level of 58% 10 minutes after gland resection, predicting a return to eucalcemia.

It is important to define the QPTH data used to predict operative outcome. As shown in Table 52-1, a true-positive QPTH result is defined as a sufficient drop in the hormone level 10 minutes after the resection of all hyperfunctioning tissue in a patient that returned to normal or low serum calcium levels lasting at least 6 months after parathyroidectomy. A true-negative result is present when the hormone level fails to fall below 50% at the 10-minute interval and the patient remains or returns to hypercalcemia within

6 months following parathyroidectomy. A true-negative QPTH result is also defined as a PTH level that does not drop below 50% after resection of a parathyroid gland or a mistaken nonparathyroid tissue, thus avoiding operative failure by pointing out the presence of MGD or missed overactive gland(s). A false-positive result is determined if the hormone level drops 50% or more but the patient has persistent hypercalcemia within 6 months after resection. The visualization of an enlarged, but normally functioning, parathyroid gland after the excision of a single tumor followed by a sufficient hormone level drop is not considered a false-positive result. A false-negative result is defined if the PTH level does not drop in 10 minutes and the patient has a successful return to low or normal calcium levels lasting at least 6 months. Hormone levels that drop in 20 minutes or later after gland excision in a postoperative eucalcemia patient are also considered false-negative QPTH results. Occasionally, these delayed drops influenced the surgeon to discontinue the cervical exploration but are considered false negative when analyzing results. Table 52-1 shows how the QPTH results, with the described criteria to predict postoperative calcium levels, are defined.

The criterion published from this institution has matured over the years, becoming more accurate in predicting operative outcome. The present criterion no longer requires a

TABLE 52-1. Evaluation of Intraoperative Parathyroid Hormone Dynamics with Assay and Criterion Selected for Predicting Postoperative Calcium Levels*

Result

PTH Decrease > 50% from Highest Preincision or Pre-excision Level 10 Minutes after Gland Resection

Postoperative Total Serum Calcium

True positive

+

Eucalcemia (<10.3 mg/dL)

True negative

Hypercalcemia (>10.3 mg/dL)

False positive

Hypercalcemia (>10.3 mg/dL)

False negative

-

Eucalcemia (<10.3 mg/dL)

'This interpretation of intact parathyroid hormone (PTH) changes during parathyroidectomy resulted in a sensitivity of 98%, specificity of 97%, positive predictive value of 99%, negative predictive value of 90%, and overall accuracy of 97% in 401 patients with sporadic primary hyperparathyroidism.

'This interpretation of intact parathyroid hormone (PTH) changes during parathyroidectomy resulted in a sensitivity of 98%, specificity of 97%, positive predictive value of 99%, negative predictive value of 90%, and overall accuracy of 97% in 401 patients with sporadic primary hyperparathyroidism.

drop in the hormone level at 10 minutes after tumor resection below the preoperative (preincision) level as stated in the past.2 If a drop below the preincision level is required 10 minutes after gland resection, a decrease in test sensitivity with an increase of the number of false-negative results is encountered. The use of such a requirement would mislead the surgeon to perform further exploration in many patients already successfully treated. The pre-excision sample should be taken specifically just before clamping the gland blood supply and not when the parathyroid is identified or during surgical manipulation.3'827 Some authors require a return to a normal range of PTH levels after resection to predict operative success.4-19 Our experience in 401 patients using the assay to guide parathyroidectomy has shown that hormone dynamics calculated as a percentage change between the levels during the operation is more accurate in predicting operative outcome than a return of the PTH levels to normal range. Furthermore, the quick assay is not reliable for absolute values of PTH in the lower range of the assay standard curve. Variation of the "quick assay" values expressed in picograms per milliliter is often present when compared with the standard 2-hour assay, even though the coefficient correlation is excellent.

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