Final answer:
In primary hyperparathyroidism, high calcium levels are present due to increased production of PTH, causing increased calcium reabsorption in the kidneys and intestines, as well as calcium release from the bones.
Step-by-step explanation:
In the case of primary hyperparathyroidism, you would find high calcium levels in the blood. Primary hyperparathyroidism is typically caused by overactivity of one or more of the parathyroid glands, which leads to excessive production of parathyroid hormone (PTH). When PTH levels are high, calcium is reabsorbed from the kidneys, the absorption of calcium from the intestines is increased, and calcium is released from the bones, all of which contribute to hypercalcemia, or elevated blood calcium levels. Consequently, phosphate levels usually decrease because PTH reduces the reabsorption of phosphate in the kidneys, promoting its excretion.