Correlation between serum calcium levels and dual-phase (99m)Tc-sestamibi parathyroid scintigraphy in primary hyperparathyroidism

Aim: The goal of the study is to correlate serum calcium levels with the results of dual‐phase ^99mTc‐sestamibi parathyroid scintigraphy to find the best cut‐off level of the serum calcium that correlates with a positive presurgery. Methods: In 111 patients, serum calcium and plasma parathormone (PTH) levels were compared with the results of the ^99mTc‐MIBI scintigraphy and with this data determined the level of calcium above which the ^99mTc‐MIBI scintigraphy was likely to be positive and below which the study was likely to be negative. Results: In total, 11 men (18%) and 50 women (82%) had a positive ^99mTc‐MIBI study. Overall 67% of those patients with a positive ^99mTc‐MIBI study had a PTH >200 ng l^?1 compared to only 9% of those with a negative ^99mTc‐MIBI scintigraphy; however, for those with a positive study on an early ^99mTc‐MIBI scintigraphy, this rose to 85%. Overall a serum calcium of >2·70 mmol l^?1 was found in 82% of patients with a positive ^99mTc‐MIBI study but only 14% of those with a negative ^99mTc‐MIBI study, this is rose to 97% of patients with a parathyroid adenoma identified on early images. It is also shown that patients whose serum total calcium <2·51 mmol l^?1 rarely have positive ^99mTc‐MIBI scintigraphy. Conclusion: ^99mTc‐MIBI parathyroid scintigraphy is most likely to yield identification and localization of a parathyroid adenoma when both PTH and calcium are elevated; however, although there is no lower limit of PTH which can predict a negative study, we cannot recommend ^99mTc‐MIBI parathyroid scintigraphy if the serum calcium is <2·51 mmol l^?1.