BACKGROUND: Predicting a multiple gland disease (MGD) in primary hyperparathyroidism (pHPT) remains challenging. This study aimed to evaluate predictive factors for MGD. METHODS: A retrospective chart review was performed of 1211 patients with histologically confirmed parathyroid adenoma or hyperplasia between 2007-2016. Localization diagnostics, laboratory parameters, and the weight of the resected parathyroid glands were evaluated concerning their predictive value of a multiple-gland disease. RESULTS: A number of 1111 (91.7%) had a single-gland disease (SGD), and 100 (8.3%) a multiple-gland disease (MGD). US and MIBI scans were comparable for either negative or positive adenoma localization and suspected MGD. While the PTH level was similar, the calcium level was higher in SGD (2.8 mmol/L versus 2.76 mmol/L, P=0.034). MGD had a significantly lower gland weight (0.78 g versus 0.31 g
P<
0.001). A gland weight of 0.418 grams was a predictive factor for MGD with a sensitivity of 72% and a specificity of 66%. CONCLUSIONS: Only the weight of the resected parathyroid adenoma was meaningful in predicting MGD. A cut-off value of 0.418 g can differentiate SGD from MGD.