Serum PTH reference values in an adult Brazilian population: implications for the diagnosis of hyperparathyroidism

ABSTRACT Objective: To define serum parathyroid hormone (PTH) reference values in carefully selected subjects following the recommended pre-analytical guidelines. Subjects and methods: First, 676 adults who would be submitted to thyroidectomy were evaluated. Patients using interfering medications or with malabsorption syndrome, hypomagnesemia, hyper- or hypophosphatemia, hypo- or hypercalcemia, 25-hydroxyvitamin D 65 pg/mL, the upper limit of normal according to the manufacturer of the kit, was observed in only one subject (0.3%). Considering the upper limit proposed by the kit's manufacturer, 1/6 hypercalcemic patients and 4/8 normocalcemic patients with PHPT had normal PTH. Using the upper limit established in this study, only one normocalcemic patient had normal PTH. Thus, the sensitivity of PTH in detecting asymptomatic primary hyperparathyroidism (PHPT) using the values recommended by the kit and established in this study was 64% and 93%, respectively (50% versus 87.5% for normocalcemic PHPT). Conclusion: The upper reference limit of PTH obtained for a rigorously selected sample was 20% lower than that provided by the assay, which increased its sensitivity in detecting PHPT.