[Parathyroid response to EDTA: effect of the immune heterogeneity of the parathyroid hormone]

The parathyroid response to EDTA infusion was measured in 23 patients with hypo- or hyperparathyroidism using two different antisera, one predominantly anti COOH-terminal (GP 62) and the other predominantly anti NH2-terminal (WC), and was compared with the responses observed in 16 controls for GP 62 and 18 controls for WC. In primary hyperparathyroidism elevated basal PTH values were found more frequently with GP 62 (6 of 10 cases) than with WC (3 of 9 cases). However, WC more frequently exhibited exaggerated responses to EDTA (8 of 9 cases) than GP 62 (7 of 10 cases). In hypoparathyroidism the basal values were not distinguishable from the normals. However, the EDTA test showed absent or low responses in 10 of 11 cases studied with GP 62. Antiserum WC showed normal responses in 4 cases with postoperative hypoparathyroidism, revealing some residual PTH secretion but not response in the 2 cases with idiopathic hypoparathyroidism. Since one of them had a normal response when measured with GP 62, secretion of an immunologically abnormal PTH may be suspected. In chronic renal failure normal responses can be observed despite an abnormal basal PTH level, since it is falsely elevated by the accumulation of COOH-terminal fragments.