# Using ex vivo radioactivity measurement to differentiate parathyroid single-gland and multigland disease

## TL;DR

This study shows that measuring radioactivity from removed parathyroid glands can quickly and reliably predict whether a patient has single or multiple overactive glands, helping surgeons make better decisions during surgery.

## Contribution

The study introduces a validated threshold (RR of 1.2) for ex vivo radioactivity measurement to distinguish single-gland from multigland disease in parathyroidectomy.

## Key findings

- Patients with single-gland disease had significantly higher radioactive ratios (RR) than those with multigland disease.
- A radioactive ratio threshold of 1.2 achieved a 92.3% positive predictive value in a validation cohort.
- Ex vivo radioactivity measurement is a reliable and time-efficient tool for intraoperative decision-making.

## Abstract

Radioguided parathyroidectomy is based on the principle that hyperfunctioning parathyroid glands have increased radiotracer uptake, which can be measured instantaneously. We sought to determine if ex vivo radioactivity measurement could be used to predict parathyroid pathology and guide surgical decision-making in a time-efficient manner.

Materials and Methods: We retrospectively reviewed patients with primary hyperparathyroidism who underwent parathyroidectomy at our institution (2000-2022). All patients received a preoperative injection of 10mCi of 99Tc. Intraoperatively, radioactivity was measured by a gamma counter within 5 seconds. The ratio of radioactive counts of resected parathyroid glands (ex vivo) to background thyroid tissue (radioactive ratio [RR]) was calculated. Patient demographics, preoperative laboratory measurements, and RRs were compared between patients with single-gland disease (SGD) versus multigland disease (MGD). The predictive threshold for SGD was subsequently validated on the following cohort of 115 patients.

Of 2368 patients included, 1585 (66.9%) patients had SGD, and 783 (33.1%) had MGD. Patients with SGD had higher median (IQR) RRs than the MGD group (0.8 [0.5-1.3] vs 0.4 [0.3-0.7], P <.001). After adjusting for age, preoperative calcium and PTH, reoperative parathyroidectomy, and gland weight, the RR was an independent predictor (OR 2.155, P <.001) of SGD. A receiver operating characteristic curve was plotted using the RR to predict the likelihood of SGD. The positive predictive value (PPV) reached a plateau at 85.3% when RR was 1.2. When the threshold of 1.2 was used in the validation cohort, the PPV was 92.3%.

Ex vivo radioactivity measurement provides an instantaneous and reliable prediction of parathyroid pathology, which could be used as an adjunct to guide surgical decision-making during parathyroidectomy.