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.