Quantification of circulating intact PTH assists in the differential diagnosis of hypercalcermia and hypocalcemia. In conjunction with the measurement of ionized calcium, intact PTH evaluations can be used to distinguish between patients with hyperparathyroidism, hypoparathyroidism, or hypercalcemia of malignancy. The diagnosis of primary hyperparathyroidism, a common cause of hypercalcemia, is confirmed by elevated ionized calcium concentrations and elevated parthyroid hormone concentrations. Intact PTH levels are also used to assess and manage other metabolic bone disorders, including osteoporosis and renal osteodeystrophy. The measurement of intact PTH using two-site immunoassays provides a more accurate assessment of parathyroid tissue secretary status, especially in patients with renal impairment.