Why do uric acid stones form?
Urate is an end product of purine metabolism. Urate solubility is pH dependent; as urine pH falls below 5.5, uric acid becomes the predominant form of urate. Uric acid is poorly soluble such that even at normal rates of urate excretion, uric acid can crystallize when urine pH is low.
In fact, most patients with uric acid stones do not over-excrete uric acid, but have an abnormally low urine pH as the cause of stone formation.
Low urine pH may be the result of high dietary intake of animal protein, chronic kidney disease (CKD), metabolic syndrome, or gastrointestinal (GI) alkali loss, as may be seen with chronic diarrhea.