In primary hyperparathyroidism, the classic laboratory triad includes which combination?

In primary hyperparathyroidism, the classic laboratory triad includes which combination?

• A. Low calcium, low PTH, high phosphate
• B. High calcium, high PTH, low phosphate
• C. High calcium, low PTH, high phosphate
• D. Low calcium, high PTH, low phosphate

Answer: (B)

The main idea is that in primary hyperparathyroidism the parathyroid glands produce too much PTH. This hormone raises serum calcium through bone resorption, increased renal calcium reabsorption, and more vitamin D activation (which boosts intestinal calcium absorption). At the same time PTH lowers serum phosphate by reducing its reabsorption in the kidneys, causing phosphate to be excreted. So the typical lab pattern is high calcium, elevated PTH, and low phosphate. This combination fits the physiology of an overactive parathyroid gland.

The main idea is that in primary hyperparathyroidism the parathyroid glands produce too much PTH. This hormone raises serum calcium through bone resorption, increased renal calcium reabsorption, and more vitamin D activation (which boosts intestinal calcium absorption). At the same time PTH lowers serum phosphate by reducing its reabsorption in the kidneys, causing phosphate to be excreted. So the typical lab pattern is high calcium, elevated PTH, and low phosphate. This combination fits the physiology of an overactive parathyroid gland.