Endocrine Abstracts

Introduction: Observed increasing frequencies of asymptomatic or oligosymptomatic PHP cases may increase the rate of false negative imaging results.

Aim: To determine the level of PTH and calcium at which an enlarged parathyroid gland can be detected by parathyroid SPECT/CT.

Material and methods: A retrospective analysis of 117 patients diagnosed with PHP (100 females and 17 males, aged 16–88 years) was performed. In each patient parathyroid SPECT/CT after administration of 500 MBq of 99mTc-MIBI was conducted (Siemens Symbia T16). Serum calcium and parathormone (PTH) were measured in each patient, serum phosphate was estimated in 109 subjects. Statistical analysis was performed with Statistica 12 Software.

Results: Median serum calcium level was 2.77 mmol/l (LQ and UQ – 2.66 and 2.87 mmol/l, respectively); median serum PTH level was 122.8 pg/ml (97.2 and 191.9 pg/ml); median plasma phosphate was 0.84 pmol/l (0.74 and 0.98 mmol/l). In 70 (59.8%) patients an enlarged parathyroid gland was detected with SPECT/CT. There was a statistically significant difference in PTH levels (median 138.15 and 114.80 pg/ml, respectively; P=0.02) and serum calcium levels (median2.74 and 2.67 mmol/l, P<0.01) between patients with positive and negative parathyroid SPECT/CT. Serum phosphate levels did not differ significantly (P=0.19). Receiver–operator curves (ROCs) were drawn to establish PTH and serum calcium cut-off levels for positive parathyroid SPECT/CT imaging. Sensitivity and specificity of parathyroid scintigraphy were 38 and 89.6%, respectively, for PTH cut-off level of 191.9 pg/ml, and 52 and 79%, respectively, for serum calcium cut-off level of 2.74 mmol/l.

Conclusions: Limiting parathyroid SPECT/CT to patients with significantly increased PTH and/or serum calcium levels, particularly if surgical treatment is not considered, may decrease false negative imaging rates and allow to avoid unnecessary radiation exposure. More precise determination of PTH and calcium cut-off levels requires analysis of larger patients group data.