Intact parathyroid hormone assay is superior to mid region assay in the EDTA-infusion test in hyperparathyroidism

We examined the use of an intact parathyroid hormone two-site immunoradiometric assay compared with a mid region parathyroid hormone radioimmunoassay in ethylene diamine tetraacetic acid-infusion test in 15 patients with hyperparathyroidism. During the test, plasma intact parathyroid hormone levels increased by 240 +/- 43%, whereas the plasma levels of mid molecule parathyroid hormone increased by only 65 +/- 17%, which is significantly lower (P less than 0.01). Four patients had no increase in plasma mid molecule parathyroid hormone level but still a large increase in plasma intact parathyroid hormone level (P less than 0.01). Thus, plasma measurement of intact parathyroid hormone is superior to that of mid molecule parathyroid hormone in the ethylene diamine tetraacetic acid-infusion test in patients with hyperparathyroidism.