PTH and hypoparathyroidism: Given that the correlation between the proportion of patients with immediate low postoperative PTH levels and permanent hypoparathyroidism is constant, extrapolating this result would suggest that a rate of 30 per cent of patients with an immediate low postoperative PTH level would correspond to a rate of 8.0 (6.0 to 10.5) per cent developing permanent hypoparathyroidism.