Predicting Failure of Conventional Imaging in Primary Hyperparathyroidism: The Impact of Parathyroid Hormone Levels and Thyroid Nodules.

BACKGROUND: Primary hyperparathyroidism (PHPT) is an endocrine disorder caused by excessive parathyroid hormone (PTH) secretion. Accurate localization remains essential for the clinical evaluation of patients; however, successful localization cannot be achieved in all patients. This study aimed to evaluate clinical and biochemical factors associated with unsuccessful localization using conventional imaging in patients with PHPT. METHODS: This retrospective cross-sectional study analyzed data from 174 patients diagnosed with PHPT between January 1, 2015, and October 1, 2024. Localization was performed using technetium-99m MIBI scintigraphy and ultrasonography; fine-needle aspiration with PTH washout was used selectively. Patients were grouped as localized (n = 127) or non-localized (n = 47) according to conventional imaging findings. Demographic characteristics, biochemical parameters, imaging results, and clinical findings were compared. RESULTS: The localized group had significantly higher intact PTH (iPTH) levels (143.0 vs 115.0 pg/mL, P < .001) and serum calcium levels (11.6 vs 11.2 mg/dL, P = .004). The non-localized group had higher age (P = .012), higher 25-hydroxyvitamin D levels (21.8 vs 17.0 ng/mL, P = .024), and more frequent thyroid nodules (74.5% vs 54.3%, P = .016). In multivariable analysis, iPTH level (OR: 1.011, 95% CI:1.002-1.020, P = .021) and thyroid nodules (OR:0.391, 95% CI:0.174-0.879, P = .023) were identified as independently associated with localization success. Receiver operating characteristic (ROC) analysis showed moderate discriminative ability of iPTH cut-off: 146.5 pg/mL (area under the curve = 0.693, sensitivity = 45.7%, specificity = 87.2%). CONCLUSION: Higher serum iPTH levels were associated with successful localization, whereas the presence of thyroid nodules was associated with unsuccessful localization using conventional imaging. These findings may help identify patients who require more cautious interpretation of conventional imaging results and individualized consideration of additional imaging modalities. Cite this article as: Erdoğan Eroğlu C, Açık Ş, Kalan Sarı I. Predicting failure of conventional imaging in primary hyperparathyroidism: The impact of parathyroid hormone levels and thyroid nodules. Eurasian J Med. 2026, 58(4), 1492, doi: 10.5152/ eurasianjmed.2026.261492.