Diagnostic for hyperparathyroidism-Elevated parathyroid hormone levels in conjunction with elevated calcium levels Essential to the diagnosis of hyperparathyroidism is the finding of hypercalcemia. All forms of hyperparathyroidism are characterized by elevated PTH levels. Primary hyperparathyroidism: Caused by increased secretion of Parathyroid hormone (PTH) from abnormal parathyroid gland, Hypercalcemia results from abnormally active parathyroid glands. Secondary hyperparathyroidism: Hypocalcaemia results in reactive overproduction of PTH. Usually occurs in association with Chronic renal failure (CRF), may occur in Hypocalcaemia secondary to inadequate calcium or vitamin D intake or in patients of malabsorption Teiary hyperparathyroidism: Hypercalcemia results from untreated sHPT, with continuously elevated PTH levels. Hyperparathyroidism is by far the most prevalent causes of hypercalcemia. The majority of patients with primary hyperparathyroidism have a single parathyroid adenoma, which can be localized with sestamibi scanning. - Technetium 99m-labeled sestamibi is taken up by the parathyroid and thyroid glands. - Hyperfunctioning parathyroid glands take up the sestamibi to a greater extent than normal glands, and therefore sestamibi scanning can be used to identify parathyroid adenomas. - Patients with primary hyperparathyroidism have either normal or elevated urinary calcium.