Diagnostic limitations of region-specific parathyroid hormone assays in the investigation of hypercalcaemia.

Assays for N-terminus, C-terminus and mid-molecule parathyroid hormone have been assessed with respect to their sensitivity and specificity in the diagnosis of primary hyperparathyroidism (1 degree HPT). The mid-molecule assay was the most sensitive method studied and only failed to identify one out of 30 patients with histologically proven 1 degree HPT. In all three assays there was some degree of overlap between results observed in 1 degree HPT and in patients with non-parathyroid hypercalcaemia, with results in the latter group sometimes falling well within the hyperparathyroid range. This study highlights the limitations of currently available methods and emphasises the need for caution in the interpretation of parathyroid hormone (PTH) measurements.