New parathyroid function index for the differentiation of primary and secondary hyperparathyroidism: a case-control study

Background Patients with primary hyperparathyroidism (PHPT) may be asymptomatic, and some may present with normocalcemic PHPT (NPHPT). Patients with vitamin D deficiency may also be asymptomatic, with normal calcium and elevated PTH concentrations. These latter patients are usually diagnosed with vitamin D deficiency-induced secondary hyperparathyroidism (VD-SHPT). Therefore, it is very difficult to distinguish PHPT and NPHPT from VD-SHPT based on calcium or PTH concentrations in clinical settings. In this case-control study, we aimed to verify the diagnostic power of a new parathyroid function index (PFindex = Ca*PTH/P).