Which renal process is increased in hypercalcemia?

Which renal process is increased in hypercalcemia?

• A. ↓ phosphate excretion
• B. No change in phosphate excretion
• C. ↑ phosphate excretion
• D. Hyperphosphatemia

Answer: (C)

The concept being tested is how parathyroid hormone (PTH) regulates renal phosphate handling, producing phosphaturia. PTH acts on the proximal tubule and inhibits the Na+-phosphate cotransporter, reducing phosphate reabsorption. This leads to more phosphate being excreted in the urine. In hypercalcemia, especially when driven by elevated PTH (as in hyperparathyroidism), this phosphaturic effect is prominent, so renal phosphate excretion increases and serum phosphate tends to fall. Different contexts where PTH is suppressed would not produce the same increase in phosphate excretion, reinforcing why increased phosphate excretion is the correct response in this scenario.

The concept being tested is how parathyroid hormone (PTH) regulates renal phosphate handling, producing phosphaturia. PTH acts on the proximal tubule and inhibits the Na+-phosphate cotransporter, reducing phosphate reabsorption. This leads to more phosphate being excreted in the urine. In hypercalcemia, especially when driven by elevated PTH (as in hyperparathyroidism), this phosphaturic effect is prominent, so renal phosphate excretion increases and serum phosphate tends to fall. Different contexts where PTH is suppressed would not produce the same increase in phosphate excretion, reinforcing why increased phosphate excretion is the correct response in this scenario.