Normocalcemic primary hyperparathyroidism (NPHPT) is diagnosed in the setting of elevated PTH concentrations with consistently normal albumin-adjusted and ionized serum calcium levels, in absence of secondary causes for elevated PTH concentrations. In order to confirm persistence of the hyperparathyroid state, PTH levels should be elevated on at least two occasions over a 3 to 6 months period. The prevalence of NPHPT depends on the population studied. Data from different studies are often not comparable; indeed, different criteria have been used to exclude secondary hyperparathyroidism. Notwithstanding such limits, the prevalence of NPHPT in studies including ionized calcium dosage was between 0.5% and 0.7%. Available data suggest that patients with NPHPT are likely to have more skeletal, kidney and metabolic complications compared to healthy subjects, but almost all studies suffer from possible misclassification of patients due to lack of ionized calcium dosage. The management of NPHPT is controversial in part due to lack of solid data about the natural history. However, surgical treatment is currently performed more frequently than in the past, although studies do not show, so far, a clear benefit from intervention.
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