[18-year-old patient with hypercalcemia, hypophosphatemia, nephrocalcinosis and normal iPTH values. Primary...

We report an 18-year old woman with surgically proven primary hyperparathyroidism (pHPT) and normal intact parathyroid hormone (iPTH) serum levels. The reason for this rare biochemical presentation are possible biologically active amino-terminal parathyroid hormone polypeptide fragments not detected by the widely used two-site immunoradiometric parathyroid hormone assay (PTH IRMA). Diagnosis and therapy of primary hyperparathyroidism therefore should not exclusively rest on the finding of hypercalcemia coupled with an elevated iPTH level.