What are the chemical precursors of renal stones?
Relatively high concentrations of salt and acid solutes determine crystalluria and stone formation. Calcium oxalate is most common and is supersaturated to four to five times its solubility in normal urine. Other precursors are calcium phosphate (hydroxyapatite) and calcium phosphate monohydrate (brushite). Uric acid, cystine, struvite (magnesium ammonium phosphate), and mucoprotein are undersaturated stone precursors. Drugs, such as ascorbic acid (conversion to oxalate) and triamterene (nidus for stone formation), also may promote renal stone formation.