Rapid parathyroid hormone analysis during venous localization

Abstract

Objective: To determine the usefulness of the rapid parathyroid hormone (PTH) assay during venous localization for primary hyperparathyroidism (1 degrees HPTH).

Summary background data: Remedial exploration for persistent 1 degrees HPTH poses a significant challenge when noninvasive preoperative localization studies are negative. Based on experience with the intraoperative rapid PTH assay, this technique was extrapolated to the interventional radiology suite and generated near real-time data for the interventional radiologist employing on-site hormone analysis, with a 12-minute turnaround time from blood sampling to assay result.

Methods: Between November 1997 and July 2002, 446 patients with 1 degrees HPTH were referred for treatment. Of these, 56 (12.5%) represented remedial patients who had each undergone one or more previous cervical explorations. Noninvasive imaging studies were positive for or suggestive of localized disease in 49/56 (87.5%) of these patients, who therefore proceeded directly to surgical exploration. Seven patients with persistent 1 degrees HPTH and negative noninvasive studies underwent selective venous sampling employing a rapid PTH assay in the interventional suite.

Results: Venous localization demonstrated an apparent PTH gradient in six of the seven patients. In three, a subtle gradient demonstrated in near real-time prompted additional sampling, which confirmed an unequivocal hormone gradient. In an additional case, the absence of a gradient on initial sampling prompted further sampling, which was positive. All of the patients were explored, and in five of the six patients with a positive PTH gradient, a parathyroid adenoma (mean weight 636 +/- 196 mg) was resected from a location predicted by venous localization. In the sixth patient with a positive gradient, parathyroid tissue was not identified; however, there was a significant fall in the intraoperative PTH values, and immediate postoperative and follow-up laboratory data at 1 month are indicative of a cure. In the one patient with negative localization, abnormal parathyroid tissue could not be located during surgical exploration.

Conclusions: The rapid PTH assay is a major adjunct for obtaining informative venous localization in patients with persistent 1 degrees HPTH. This information is extremely helpful to the surgeon in this challenging group of patients and resulted in a 100% cure rate when a venous gradient was demonstrated. The authors now employ this technique routinely in remedial patients with negative noninvasive imaging studies.

Figure 1. Venous PTH levels (pg/mL) obtained in the interventional suite employing the rapid PTH assay in patient 6. A positive gradient was not noted until sample 19 was obtained from the right superior thyroid vein (4,150 pg/mL). This was then confirmed by additional samples. At surgery a right upper ectopic parathyroid adenoma was resected from the right retroesophageal position.

Figure 2. (A) Venous PTH levels (pg/mL) obtained in the interventional suite in patient 4. A gradient was demonstrated in the right vertebral vein. (B) Highly selective catheterization of this vein and the superimposed PTH values (pg/mL). (C) Highly selective arteriography demonstrated a tumor blush (arrows).

Figure 3. (A) Pre-, intra-, and postoperative PTH (pg/mL) values for the seven patients. All patients had curative surgery, except patient 5, demonstrated by the hatched line. Multiple additional intraoperative samples were obtained in all of the patients but are not shown. Preop, preoperative sample obtained before the operative date; Baseline, baseline sample in the operating room; 10 Min, 10 minutes following parathyroid adenoma resection; 1 Week, PTH value at 1 week follow-up. (B) Location of parathyroid adenomas resected during remedial surgical exploration. The adenomas from patients 4 and 6 were retroesophageal. Numbers refer to individual patients.