Treating renal calculi in patients with a solitary functioning kidney represents an important challenge to urologists. Careful and wise treatment decisions are crucial for the complete removal of stones without causing injury to the renal tissue and/or detrimental effects on renal function [1, 16].
Attributed to the tremendous technological advancements of flexible ureteroscopes and holmium lasers, retrograde intrarenal surgery (RIRS) has gained popularity and has become one of the most accepted substitutes for PCNL and SWL in the treatment of renal calculi < 20 mm. RIRS has minimal complication rates and high stone-free rates [17, 18]. However, this procedure might need to be repeated if treating large renal stones. RIRS has an advantage in preventing renal parenchyma damage, which is critical for patients with a solitary kidney [2, 19].
In our study, the primary SFR was 84% and the final SFR was 92% while using UAS in 5 (10%) of the patients. A mean 1.08 procedures were applied per patient. This is in accordance with the studies performed by Atis et al.  (primary SFR 83%, secondary SFR 95.8%) who used UAS in 87% of their cases. Giusti et al.  (primary SFR of 72.4%, secondary SFR of 93.1%) had a mean of 1.24 procedures per patient and used UAS in 93.1% of their cases. Breda et al.  had the final overall stone-free rates of 92.2% after an average of 1.4 sessions. Gao et al.  had initial and final procedures were 64.44% and 93.33%, respectively, with a mean number of procedures of 1.23, which used UAS in all cases. In Lai et al. , the SFRs after the single and second procedures were 80% and 95%, respectively, and used UAS in all cases. Yuruk et al.  used an access sheath in 15 (83.3%) of the patients and reports stone-free rates during the 3rd postoperative month of 66.6% with the number of sessions required for stone-free status averaging 1.06 ± 0.24.
The objectives of treating renal stones in a solitary kidney are to accomplish a high stone-free rate with the lowest short- and long-term adverse effects on existing renal function. In addition to the serum creatinine, we also calculate GFR for assessment of the renal function, hence serum creatinine might be inaccurate in several situations, such as in patients with low muscle mass or with fluid overload . In our study, we noticed a momentous improvement in Scr during the 1-month follow-up while GFR not encounter any significant variation post-surgery (63.04 ± 33.16 ml/min) compared to preoperative rates (61.12 ± 34.76 ml/min, p value 0.502). The mean pre-operative Scr level was 1.76 ± 1.21 mg/dL and decreased to 1.57 ± 0.91 mg/dL post-surgery (p = 0.001). Our outcomes were proportionate with the study conducted by Kuroda e al.  and Lai et al.  who found convincing improvements in serum creatinine post-surgery, while Atis et al. , Giusti et al. , Yuruk et al. , Gao et al. , and a systematic review by Jones et al.  revealed that, despite the minimally invasive nature of RIRS, there are no changes in renal function before and after surgery.
However, it is a noninvasive procedure, yet still might be associated with major complications. In the present study, complications were assigned according to a modified clavien grading system. Perioperative complications occurred in six patients (24%), the majority of these were minor (Clavien I & II), and major complications (Clavien IIIb) occurred in one patient (4%) who developed steinstrasse after DJ removal, which necessitated surgical intervention (semi-rigid URS) to relieve the ureteric obstruction. No serious complications (higher Clavien grade) nor blood transfusion or renal failure were observed.
Atis et al.  reported a minor complication rate of 16.6%; no major complications developed in their study group. Giusti et al.  reported 27.4% of minor complications and no major complications. Gao et al.  noted postoperative complications in 26.6% of the patients, 24% of the patients had Grade I and II, and Grade III complications, and 2.2% of the patients had an anuria complication due to steinstrasse, which required urgent intervention.
Kuroda et al.  reported minor complications that included Clavien I & II in 15.8% and clavien III in 5.2% of the patients. Lai et al.  reported minor complications in nine patients (15%) and major complications (Clavien III) in two patients (3.3%). One patient developed steinstrasse and the other developed a perirenal abscess. Yuruk et al.  reported an overall complication rate of 38%, 11% were minor and 27% were Clavien IIIa (colicky pain).
Pietropaulo et al. performed a systematic review that included 12 studies that reported an overall complication rate of 16.4%, with no fatalities. Also, Clavien III complications were recorded in less than 0.5% of patients .
Jones et al., who conducted a systematic and meta-analysis review, report a total of 33 (28%) complications, a majority (n = 21) of which were Clavien grade I. The Clavien grade II/III complications were comprised of urosepsis, steinstrasse and renal colic .
According to our study, RIRS with and without using UAS is a feasible way to treat renal stones in a solitary kidney patient with high SFR. RIRS has low complication rates and does not compromise renal function.
The main drawback of this study was the short follow-up period, which made it difficult to assess the long-term effects of RIRS on renal function.