Which of the following biochemical change is seen in primary hyperparathyroidism?
Primary hyperparathyroidism is caused by overactivity of the parathyroid glands, usually a benign tumor. The main hormone involved is parathyroid hormone (PTH). The primary function of PTH is to regulate calcium and phosphate levels. So, in primary hyperparathyroidism, PTH is overproduced regardless of the body's needs.
High PTH levels lead to increased bone resorption, which releases calcium into the blood. That would cause hypercalcemia. At the same time, PTH inhibits phosphate reabsorption in the kidneys, leading to hypophosphatemia. Also, PTH increases calcium reabsorption in the kidneys, so serum calcium goes up. Another effect is on vitamin D metabolism; PTH enhances the production of active vitamin D (1,25-dihydroxyvitamin D), which increases intestinal calcium absorption. But in the context of primary hyperparathyroidism, the main issue is the elevated PTH causing these changes.
So the correct answer should be hypercalcemia and hypophosphatemia with elevated PTH. Let's look at the options. The user hasn't provided them, but common distractors might include other electrolyte imbalances. For example, hypocalcemia would be incorrect because it's the opposite. Hyperphosphatemia is also wrong since PTH causes phosphaturia. Maybe options could also include normal PTH or low PTH, which would be incorrect because in primary hyperparathyroidism, PTH is high. Another possible wrong option could be elevated phosphate with hypercalcemia, but that's not typical because PTH causes hypophosphatemia.
The clinical pearl here is that primary hyperparathyroidism is characterized by hypercalcemia, hypophosphatemia, and elevated PTH. Remembering the classic triad helps in differentiation from other causes like malignancy or vitamin D toxicity, where PTH might be suppressed. Also, the mnemonic could be "stone, bone, groan, and moan" for symptoms, but the key lab findings are the ones mentioned.
So, when explaining each section, I need to make sure the core concept is clear about PTH's role. The correct answer is hypercalcemia and hypophosphatemia with elevated PTH. The wrong options would be things like hypocalcemia, normal PTH, or hyperphosphatemia. Each of these needs a brief explanation why they're incorrect. The clinical pearl should emphasize the lab findings and their significance.
**Core Concept**
Primary hyperparathyroidism is characterized by excessive parathyroid hormone (PTH) secretion, leading to **hypercalcemia**, **hypophosphatemia**, and **elevated urinary calcium excretion**. PTH stimulates bone resorption, renal calcium reabsorption, and intestinal calcium absorption via 1,25-dihydroxyvitamin D activation.
**Why the Correct Answer is Right**
Elevated PTH directly increases serum calcium by enhancing osteoclast-mediated bone resorption and renal tubular calcium reabsorption. Simultaneously, PTH inhibits phosphate reabsorption in the proximal tubule, causing hypophosphatemia. The