Parathyroid response to EDTA in hypoparathyroidism and in tetany

The parathyroid response to an EDTA infusion was measured in 11 patients with hypoparathyroidism and 22 patients with normocalcaemic tetany, and compared to that of normal controls and of 23 patients with primary hyperparathyroidism. Despite comparable basal PTH values, the patients with hypoparathyroidism and the normocalcaemic patients, with tetany following thyroid surgery, responded less than normals to EDTA, while normocalcaemic patients with tetany due to psychogenic hyperventilation responded more than normals. In hypoparathyroidism, mainly three types of results were observed: no response (total hypoparathyroidism), diminished or delayed response (partial hypoparathyroidism), and discrepant results using different antisera in cases of idiopathic hypoparathyroidism, suggesting the secretion of immunologically abnormal PTH. In tetany due to psychogenic hyperventilation, parathyroid hyperreactivity might be explained by repeated stimulation through respiratory alkalosis. Although the EDTA test rarely improved the diagnostic accuracy of basal PTH measurements in primary hyperparathyroidism, it was useful for differentiating between latent hypoparathyroidism and tetany due to psychogenic hyperventilation, both presenting with normal plasma calcium.