Review Question - QID 101243

Decreased calcium, increased citrate, decreased oxalate, and increased free water clearance are all protective against nephrolithiasis.

The composition of urine is a critical factor in the process of crystal precipitation and stone formation. Increases in the concentrations of the stone-forming compounds calcium and oxalate can lead to the precipitation of these substances in the urine causing stones to form, while high fluid intake and an associated increase in free water clearance dilutes urine and is protective against stone formation. Urinary citrate binds ionized calcium, preventing stone precipitation and leading to calcium excretion.

Illustration A is a CT scan of a 3mm radio-opaque calcium-containing stone in the ureter (arrow).

Incorrect Answers:
Answer 1: Increased urinary calcium and oxalate favor stone formation. Both compounds can precipitate in the urine when present in high concentrations.
Answer 2: Increased urinary oxalate favors stone precipitation.
Answer 3: Decreased urinary citrate and increased oxalate favor stone precipitation.
Answer 5: Increased urinary oxalate and decreased free water clearance favor stone precipitation.