Biochemical Metrics for Parathyroid Scintigraphy in the Pre-Surgical Evaluation of Hyperparathyroidism.

Purpose: To correlate parathyroid scintigraphy results with patient biochemistry, surgery, and pathology to inform appropriateness criteria and assess biochemical metrics in the imaging workup of hyperparathyroidism.

Methods: This retrospective study included 421 patients who underwent parathyroid scintigraphy. Patients were grouped based on primary versus secondary hyperparathyroidism, and clinical profiles were reviewed for scan result, blood work, surgical results, and pathology. Performance metrics of scintigraphy were analyzed. Demographics, bloodwork, and location were compared between positive and negative scans. Predictors of positive scans were identified by multivariate logistic regression analysis. The performance of biochemistry to predict scan results was evaluated by ROC analyses.

Results: Positive tests-occurring in 52% of patients-were associated with higher parathyroid hormone (PTH) and corrected calcium. However, PTH was only predictive of a positive test in patients with secondary hyperparathyroidism. On multivariate analysis, male sex, corrected calcium, and younger age were predictors of a positive scan. Corrected calcium was the most predictive with an OR of 1.28 for every 0.1 mmol/L increase. Based on ROC analysis, corrected calcium had an AUC of 0.628 and a cutoff of 2.65 mmol/L maximized sensitivity (88%) and specificity (35%) for a positive test.

Conclusion: In this large retrospective cohort, several biochemical metrics, including corrected calcium levels, were predictive of a positive scintigraphy study. Furthermore, biochemistry, including PTH levels, significantly differed between primary and secondary hyperparathyroidism suggesting that tailored biochemical metrics are required. This work sets a foundation for the development of a robust biochemical scoring system to optimize patient selection for parathyroid imaging.