The "old" 15 mm renal stone size limit for RIRS remains a clinically significant threshold size

To investigate the performance of retrograde intrarenal surgery (RIRS) for the 1-2 cm renal stone size range in comparison to smaller stones.

From a data base of 3000 ureteroscopies between 2004 and 2014, 635 consecutive patients underwent RIRS for renal stones. Patients were divided to three groups according to their renal stone size (<10, 10-15, 15-20 mm). Preoperative, operative, stone free rate (SFR) and follow-up data were analyzed and compared.

The SFR for the three groups was 94.1, 90.1 and 85%, respectively. Patients with renal stone size above 15 mm had a statistically significantly lower SFR. The efficiency quotient calculated for stones larger and smaller than 15 mm was 83.9 vs. 91.8%, respectively (p < 0.01). The mean operative time and hospital stay were longer for patients with renal stones larger than 15 mm (73.6 ± 29.9 vs. 53 ± 19.4 min, p < 0.01 and 2.2 ± 2 vs. 1.8 ± 1.8 days, p = 0.031, respectively). Moreover, the complication rate was almost two times higher (10 vs 5.4%, p = 0.08). Concomitant ureteral stones and older age were independent predictors of failure in the large stone group.

While the overall SFR following RIRS for renal stones up to 2 cm is generally high, the SFR for 15-20 mm stones is significantly lower, with a longer operating time and hospital stay, and a higher complication rate.