**Question:** Which of the following is a feature of primary hyperparathyroidism?

A. Increased bone resorption
B. Decreased urine calcium excretion
C. Elevated serum calcium levels
D. Suppressed parathyroid hormone (PTH) levels

**Core Concept:**
Primary hyperparathyroidism is a condition characterized by the overproduction of parathyroid hormone (PTH) from one or more of the parathyroid glands. PTH plays a crucial role in maintaining calcium homeostasis by regulating calcium levels in the blood and bones. In primary hyperparathyroidism, the elevated PTH leads to increased calcium absorption from bones and increased calcium release from the kidneys, ultimately causing elevated serum calcium levels and decreased urine calcium excretion.

**Why the Correct Answer is Right:**
C. Elevated serum calcium levels is correct because in primary hyperparathyroidism, the overproduction of PTH results in increased calcium absorption from bones and increased calcium release from the kidneys. This leads to elevated serum calcium levels.

**Why Each Wrong Option is Incorrect:**
B. Decreased urine calcium excretion is incorrect because, despite elevated PTH levels in primary hyperparathyroidism, the condition ultimately leads to increased calcium absorption and release, not decreased excretion.
D. Suppressed parathyroid hormone (PTH) levels is incorrect because primary hyperparathyroidism is characterized by excessive PTH production, not suppression.
A. Increased bone resorption is correct as elevated PTH leads to increased calcium absorption from bones, which can result in bone pain, fractures, and increased bone resorption.

**Clinical Pearl:**
Primary hyperparathyroidism should be suspected in patients presenting with symptoms like bone pain, fatigue, weight loss, kidney stones, or fractures. Serum calcium and PTH levels should be evaluated, along with a bone density test to confirm the diagnosis. Treatment typically involves removing the overactive parathyroid gland through surgery, radioactive iodine therapy, or medication.