Endocrine Abstracts

Primary hyperparathyroidism (PHP) diagnosis in clinical practice is based on biochemical blood tests. Since a single parathyroid adenoma causes about 85% of cases, the treatment of choice is parathyroidectomy, preceded by imaging studies. Ultrasound and [^99mTc]sestamibi scanning can enable adenoma localization. However, the latter method is of higher sensitivity, especially if combined with anatomical imaging. In some cases, the radiotracer uptake in adenoma tissue is insufficient, leading to negative imaging results. This study aimed to compare parathormone (PTH), calcium, and serum phosphate levels among patients diagnosed with PHP with positive and negative parathyroid nuclear hybrid imaging (SPECT/CT) and to evaluate biochemical parameters’ ability to predict imaging results.

Results: 563 patients with suspected primary hyperthyroidism (84% females, median age 62 years, IQR 19 years; 16% males, median age 59 years, IQR 25 years) who underwent [^99mTc]sestamibi SPECT/CT imaging between 2010 and 2022, were included in this study. The imaging result was positive in 257 cases (46%). Patients with positive imaging were characterized by higher PTH (median 124.5 pg/ml vs 96.6 pg/ml; P<0.05), higher calcium (median 2.76 mmol/l vs 2.67 mmol/l; P<0.05), and lower serum phosphate concentrations (median 0.82 mmol/l vs 0.89 mmol/l; P<0.05). Based on ROC analysis, the following threshold values for nuclear imaging were proposed for calcium, PTH, and serum phosphate concentrations, respectively: calcium ≥3.11 mmol/l (AUC 0.73; PPV 72%; sensitivity = 37%; specificity = 88%); phosphate ≤ 0.45 mmol/l (AUC 0.65; PPV 55%; sensitivity = 36%; specificity = 79%); PTH ≥ 260 pg/ml (AUC 0,70; PPV 78%; SENS = 33%; SPEC = 92%).

Conclusions: Before offering preoperative hybrid nuclear imaging to a patient with PAH, attention should be paid to the results of biochemical tests to limit unnecessary radiation exposure. Indeed, if calcium and parathormone concentrations are slightly above the upper reference values, the probability of a negative imaging result seems to be high.