Editing Kidney stone disease (section)

==== Uric acid stones ====
About 5–10% of all stones are formed from [[uric acid]].<ref name=Moe2006 /> People with certain metabolic abnormalities, including [[obesity]],<ref name=Johri2010 /> may produce uric acid stones. They also may form in association with conditions that cause [[hyperuricosuria]] (an excessive amount of uric acid in the urine) with or without [[hyperuricemia]] (an excessive amount of uric acid in the [[blood serum|serum]]). They may also form in association with disorders of acid/base metabolism where the urine is excessively acidic (low [[pH]]), resulting in precipitation of uric acid crystals. A diagnosis of uric acid [[urolithiasis]] is supported by the presence of a [[Radiodensity|radiolucent]] stone in the face of persistent urine acidity, in conjunction with the finding of uric acid crystals in fresh urine samples.<ref name=Halabe1994 />

As noted above (section on calcium oxalate stones), people with [[inflammatory bowel disease]] ([[Crohn's disease]], [[ulcerative colitis]]) tend to have [[hyperoxaluria]] and form oxalate stones. They also have a tendency to form urate stones. Urate stones are especially common after [[Colectomy|colon resection]].

Uric acid stones appear as [[Pleomorphism (cytology)|pleomorphic]] crystals, usually diamond-shaped.  They may also look like squares or rods which are polarizable.<ref name="De Mais" />