ITE Nephrology Practice Test

Phosphate balance depends on both intestinal absorption and renal handling, with vitamin D playing a key role in gut absorption and PTH regulating renal phosphate excretion. When vitamin D is deficient, the body absorbs less phosphate from the gut, and secondary hyperparathyroidism often follows, which increases phosphate wasting in the kidneys. The combination lowers serum phosphate, making hypophosphatemia likely. The other options don’t directly cause a drop in phosphate: hyperkalemia, hypernatremia, and hypercalcemia don’t characteristically drive phosphate down via the same gut absorption or renal excretion mechanisms.