Appropriate kidney stone size for ureteroscopic lithotripsy:When to switch to a percutaneous approach

Flexible ureteroscopy(f URS) has become a more effective and safer treatment for whole upper urinary tract stones. Percutaneous nephrolithotomy(PNL) is currently the first-line recommended treatment for large kidney stones ≥ 20 mm and it has an excellent stone-free rate for large kidney stones. However, its invasiveness is not negligible considering its major complication rates. Staged f URS is a practical treatmentfor such large kidney stones because f URS has a minimal blood transfusion risk, short hospitalization and few restrictions on daily routines. However, as the stone size becomes larger, the stone-free rate decreases, and the number of operations required increases. Therefore, in our opinion, staged f URS is a practical option for kidney stones 20 to 40 mm. Miniaturized PNL combined with f URS should be considered to be a preferred option for stones larger than 40 mm. Moreover, URS is an effective treatment for multiple upper urinary tract stones. Especially for patients with a stone burden < 20 mm, URS is a favorable option that promises a high stone-free rate after a single session either unilaterally or bilaterally. However, for patients with a stone burden ≥ 20 mm, a staged operation should be considered to achieve stone-free status.