Performance and Clinical Utility of a Commercially Available ‘C-terminal’ PTH Assay

Abstract

SUMMARY. The performance and clinical utility of a 'C-terminal' parathyroid hormone (PTH) radioimmunoassay (Dac-Cel, Wellcome Diagnostics) is described. Parathyroid hormone, as measured by the Dac-Cel method, is stable in whole blood samples for at least 24 h. 84% of patients with hypercalcaemia due to primary hyperparathyroidism have values above the upper limit seen in normocalcaemic subjects (0,5 ug/L), with detectable serum PTH demonstrable in the remaining 16%. In patients with hypocalcaemia due to hypoparathyroidism serum PTH was undetectable in 73% and 'inappropriately' low in the remainder. In 50% of patients with malignancy-associated hypercalcaemia serum PTH was undetectable, but was above 0·5 ug/L in 13%. Increased PTH concentrations were invariably found in patients with renal failure.The Dac-Cel method is a reliable and robust technique for measurement of PTH and in conjunction with determination of calcium facilitates the diagnosis of primary parathyroid disorders. Caution is required in the interpretation of PTH measurements in patients with renal failure; the significance of detectable PTH in some patients with malignancy-associated hypercalcaemia is not clear.Determination of serum immunoassayable parathyroid hormone (PTH) concentrations forms an important part of the investigation of disorders of calcium metabolism. However, measurement of circulating PTH by radioimmunoassay (RIA) has been bedevilled by the heterogenous nature of circulating PTH and its peripheral metabolism. In recent years, improved understanding of the physiology of PTH secretion and its metabolism, together with the use of well-characterised antisera, has facilitated interpretation of results of PTH in serum. In this report we have evaluated the use of a recently available commercial 'C-terminal' PTH assay (Dac-Cel, Wellcome Diagnostics, Temple Hill, Dartford DA1 5AH, UK) in the investigation of patients with disorders of calcium metabolism. MethodsDac-Cel PTH RIA kits were supplied by

A comparison of the performance andclinical utility of mid‐molecular and C‐terminalparathyroid hormone assays

“…Studies reported here and in a previous publication [5] indicate the stability of both mid-molecule and C-terminal fragments of PTH in serum.…”

“…Ingle et al [5] have previously reported data showing the stability of C-terminal PTH fragments in serum. No significant change in PTH occurred in serum left at room temperature for 24 h, even if not centrifuged and separated, and no significant change in PTH was reported after one, two or three freeze thaw cycles.…”

Clinical and Laboratory Evaluation of a Two-Site Immunoradiometric Assay for Intact Parathyroid Hormone

“…This contrasts with results previously reported in assays specific for the N-terminus,13 mid-region': 13 and C-terminus. 6 • 13. 14 However, in contrast to the results presented in the initial clinical evaluation of this assay, 4 intact PTH concentrations were suppressed in only 56% of patients in this category with the remainder having levels which fell well within the reference range.…”

Anomalies in the Assay of Parathyroid Hormone in Normocalcaemic Patients With Renal Stone Disease

“…'251-bovine PTH was used as the radioligand and the assay was calibrated against bovine PTH standards (Dac-Cel PTH, Wellcome Diagnostics). The assay reference range, < 200-600 ng/l, was based on manufacturers limits confirmed independently in 62 normal subjects (Ingle et al, 1986). The interassay coefficient of variation was 6%.…”