Crohn’s disease with diarrhea predisposes to calcium oxalate stones primarily because of enteric hyperoxaluria from fat malabsorption and saponification resulting in usage of calcium and less formation of insoluble calcium oxalate salts in the intestinal lumen. There is thus increased gastrointestinal oxalate absorption leading to increased urinary oxalate excretion. Other factors include increased oxalate colonic mucosa permeability and gastrointestinal tract decolonization of the oxalate-fermenting bacterium Oxalobacter formigenes. It also predisposes to uric acid stones as a consequence of gastrointestinal bicarbonate loss from diarrhea and acidified urine secondary to metabolic acidosis.
