Background: Since the demonstration that the second-generation PTH assays, also called "intact" PTH assays, recognize a (non 1-84) PTH fragment in addition to the intact 1-84 PTH, new PTH assays defined as third-generation assays have been commercialized. Two previous studies aimed at evaluating whether these third-generation PTH assays improved the diagnostic sensitivity for primary hyperparathyroidism (PHPT), but they yielded opposite results.

Methods: In the present study, we compared two second-generation PTH assays (the total intact PTH assay from Scantibodies Laboratory Inc. and the Intact PTH assay from Nichols Institute Diagnostics), with two third-generation assays (the Cyclase Activating PTH assay also from Scantibodies Laboratory and the Bio-intact PTH assay from Nichols Institute), in a series of 145 consecutive PHPT patients operated in our Endocrine Surgery department over a 10-month period. A group of 74 healthy subjects served as controls.

Results: The diagnostic sensitivity for PHPT of the Total intact, the Intact, the Cyclase Activating, and the Bio-intact assays was 93.8%, 97.3%, 84.2%, and 89.0% respectively, with a 95% confidence interval in the control group of 10-46, 11-60, 8.4-34 and 9-41 ng/L, respectively.

Conclusion: Our findings demonstrate that the diagnostic sensitivity of second and third-generation PTH assays are similar. Third generation PTH assays do not therefore improve the diagnosis of elevated serum PTH levels in PHPT, although there are numerical differences among the values.

Key-words: parathyroid hormone, primary hyperparathyroidism, immunoassays, reference values, vitamin D.