Which hormone is typically found in excess in patients with primary hyperparathyroidism?

In patients with primary hyperparathyroidism, there is an overproduction of parathyroid hormone (PTH) primarily due to a benign tumor on one of the parathyroid glands or hyperplasia of the glands. This condition results in an excessive release of PTH into the bloodstream, which plays a critical role in regulating calcium levels in the body. PTH increases osteoclast activity leading to increased bone resorption, enhances renal tubular reabsorption of calcium, and promotes the conversion of vitamin D to its active form, ultimately resulting in increased serum calcium levels. The elevated PTH levels distinguish primary hyperparathyroidism from other conditions that might also affect calcium metabolism, such as secondary hyperparathyroidism, where PTH is elevated in response to low calcium levels. Thus, the presence of excess PTH is a hallmark of primary hyperparathyroidism, making it the correct answer in this scenario.