THE VALUE TO THE SURGEON OF PARATHYROID HORMONE ASSAYS IN PRIMARY HYPERPARATHYROIDISM

The role of various parathyroid hormone (PTH) radio‐immunoassays in the diagnosis of primary hyperparathy‐roidism (PHP) is controversial. A series of 204 patients with surgically proven PHP was studied. Serum total calcium, serum ionized calcium, amino (N)‐terminal PTH and carboxyl(C)‐terminal PTH were assessed in relation to the volume and weight of adenomatous or hyperplastic parathyroid tissue excised at operation. N‐terminal PTH was elevated above the normal laboratory range in only 24% of patients and correlated relatively poorly with the volume of abnormal parathyroid tissue (r = 0.20, P= 0.05). C‐terminal PTH was elevated above the normal range in 91% of patients and had a strong correlation with the volume of abnormal parathyroid tissue (r = 0.63, P< 0.001). The correlation coefficients between C‐terminal PTH and serum total calcium and serum ionized calcium were both 0.63 (P< 0.001). In contrast, there was no correlation between N‐terminal PTH and serum total calcium (r= ‐0.02), serum ionized calcium (r= ‐0.04) or C‐terminal PTH (r = 0.09). A combination of hypercalcaemia and elevated C‐terminal PTH can be regarded as strong diagnostic evidence of PHP. Furthermore, the level of C‐terminal PTH can assist the surgeon by approximately predicting the amount of adenomatous or hyperplastic parathyroid tissue that may be expected at surgical exploration.