Why do patients with bowel disease have a higher risk of kidney stone formation?
Diarrheal states cause low urine flow, as patients lose excess water from the GI tract, and patients may restrict fluid intake to lower GI output. In addition, chronic diarrhea leads to GI bicarbonate loss, causing metabolic acidosis.
The acidosis leads to low urine pH, a risk factor for uric acid stones, and low urine citrate, a risk factor for calcium stones.
These abnormalities are commonly found in patients who have colectomy, with or without ileostomy. If a patient has fat malabsorption from Crohn disease or small bowel surgery, they can develop enteric hyperoxaluria, as steatorrhea leads to increased oxalate absorption in the colon.
Note that enteric hyperoxaluria does not occur in patients who have had a colectomy.