<qa>  What is the risk factor for calcium nephrolithiasis?Extracorporeal shock wave lithotripsy ESWL and Percutaneous nephrolithotomy PCNL become the therapy of choice for renal stone. Although providing good results, stone recurrence is usually found as the therapies do not change the underlying metabolic abnormality. Among the metabolic disorders, hypocitraturia is an important risk factor for calcium nephrolithiasis. This study evaluate the preventive effects of potassium sodium citrate on stone recurrence as well as stone growth post ESWL or PCNL, in patients with calcium-containing stones. 