Association Between Biochemical Parameters, Parathyroid Gland Morphometry, and Dual-Phase MIBI SPECT/CT Findings in Primary Hyperparathyroidism

<b>Objective</b>: This study assessed the relationship between serum calcium (Ca) and parathyroid hormone (PTH) levels, the size and weight of the enlarged parathyroid gland (PG), and the results of technetium-99m-metoxyisobutylisonitrile (MIBI) parathyroid scintigraphy with single-photon emission computed tomography/computed tomography. <b>Methods</b>: Among 252 patients who underwent surgery for hyperparathyroidism between October 2022 and March 2025 at the Department of Endocrine Surgery of the University Hospital in Krakow, 212 patients with primary hyperparathyroidism (PHPT) were selected and divided into the MIBI(-) (n = 49) and MIBI(+) (n = 163) groups. <b>Results</b>: MIBI was positive in 76.9% and negative in 23.1% patients with PHPT. Mean PTH in the MIBI(+) and MIBI(-) groups was 177.3 ± 144.7 and 127.7 ± 59.4 pg/mL, respectively. Significant differences were found in PTH (<i>p</i> < 0.01), maximum excised PG size (<i>p</i> < 0.01), and weight (<i>p</i> < 0.01). PTH predicted positive scintigraphy in univariate analysis (OR = 2.65; 95% CI: 1.19-5.89; <i>p</i> = 0.02) and showed a borderline association in the multivariate model (OR = 2.47; 95% CI: 0.95-6.41; <i>p</i> = 0.06). Optimal cut-offs for predicting MIBI positivity were 135.0 pg/mL for PTH (AUC = 0.64), 0.73 g for PG weight (AUC = 0.81), and 18.0 mm for PG maximum size (AUC = 0.78). The Wisconsin index (Ca × PTH) was associated with positive MIBI (OR = 2.58; 95% CI: 1.15-5.78; <i>p</i> = 0.02), with an optimal cut-off of 256.0. Serum total Ca levels showed no significant association with positive MIBI (<i>p</i> = 0.60). <b>Conclusions</b>: Serum PTH levels, Wisconsin index, and enlarged PG size and weight may help predict parathyroid scintigraphy outcomes.