Associations of Serum Ionized Calcium, Phosphate, and Pth Levels with Parathyroid Scan in Primary Hyperparathyroidism

Abstract

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). 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. 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. 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. BMI = body mass index; CT = computed tomography; CV = coefficient variation; DXA = dual-energy x-ray absorptiometry; MRI = magnetic resonance imaging; PHPT = primary hyperparathyroidism; PPV = positive predictive value; PTH = parathyroid hormone; SPECT = single-photon emission computed tomography; Tc = technetium-99 sestamibi.