Associations of serum ionized calcium, phosphate, and PTH levels with parathyroid scan in primary hyperparathyroidism

Objective: To evaluate the relationship between various biochemical parameters in patients with primary hyperparathyroidism (PHPT) with positive and negative technetium-99 sestamibi (Tc) parathyroid scans performed with single-photon emission computed tomography/computed tomography (SPECT/CT). Methods: This retrospective analysis was used to develop a logistic probability model. It included 218 patients with PHPT. The main outcome measures were serum total calcium, ionized calcium, intact parathyroid hormone (PTH), albumin, alkaline phosphatase, phosphate, 25-hydroxy vitamin D, 1,25-dihydroxy vitamin D, 24-h urinary calcium levels, and parathyroid adenoma weight. Results: Individually, using cut-off levels of 6.0 mg/ dL for ionized calcium, 3.0 mg/dL for phosphate, and 90 pg/mL for intact PTH, we found that 91.3% (P = .005), 70.7% (P = .004) and 87.90% (P = .023) of the patients had a positive Tc scan with their corresponding strengths of associations in the parentheses. Similar significant associations were sustained in multivariate setting for serum ionized calcium (P = .015), phosphate (P = .016), and intact PTH (P = .028). A logistic probability model was designed to predict the probability of being positive for Tc scan given a set of covariates. Conclusion: There are significant associations between the levels of serum ionized calcium, phosphate, intact PTH, and Tc scan positivity. Further studies with larger patient populations are needed.