From January 2022 to December 2023, 166 patients were randomized into two groups: 82 who underwent PCNL and 84 who underwent NP-URL-FU, with a mean age of 48.1 ± 12.9 years. Of these, 72.9% were male. The demographic data and preoperative variables are presented in Table 1. The NP-URL-FU group had a higher proportion of left-sided stones, single-stone load, and mild hydronephrosis (P < 0.05). They also had smaller stone lateral and longitudinal diameters as well as lower CT_HU values (P < 0.05) than those in the PCNL group. No significant differences were found between the groups in terms of patient age, sex, body mass index, stone location, preoperative blood WBC count, Hb, Cr, urinary WBC count, nitrite, urine culture, BUN, PCT, or CRP levels (all P > 0.05).

Univariate analysis of the association between stones and SFR factors (7 days and 2 months) is shown in Table 2. Stone location, preoperative Hb level, preoperative urinary WBC count, surgical method, and SFR at 7 days varied significantly (P < 0.05). Stone size (i.e., lateral and longitudinal diameters), stone location, stone load, preoperative Hb level, preoperative urinary WBC count, and SFR at 2 months also showed significant variations (P < 0.05).

Three logistic regression models were established to analyze the relationship between the surgical method and the 7-day (Table 3) and 2-month SFR (Table 4). Table 3 indicated an 86%(OR = 0.14, 95% CI 0.07–0.29 decrease in the risk of 7-day SFR in the NP-URL-FU group as compared to the PCNL group; after adjustment, the results remained stable. However, there was no statistically significant association between the surgical method and the 2-month SFR. To verify the stability of the results, subgroup analyses (Table 5)were conducted; no significant interactions were observed.

We also found notable results regarding stone location. As compared to other locations (upper, middle, and renal pelvis), the lower-calyx-stones group had a 7-day SFR decrease of 58% (OR = 0.42, 95% CI 0.22–0.80), 60% (OR = 0.40, 95% CI 0.21–0.78), and 69% (OR = 0.31, 95% CI 0.12–0.79), respectively. The 2-month SFR was not statistically significant after full adjustment.

For every 1-unit increase in preoperative Hb, the risk of being stone-free increases by 2% (OR = 1.02, 95% CI 1–1.04), 3% (OR = 1.03, 95% CI 1.01–1.06), and 4% (OR = 1.04, 95% CI 1.01–1.08) at 7 days, and by 2% (OR = 1.02, 95% CI 1–1.04), 3% (OR = 1.03, 95% CI 1–1.05), and 5% (OR = 1.05, 95% CI 1.01–1.09) at 2 months, indicating that a good physical condition was associated with a better prognosis.

As compared to the negative group, the positive group for preoperative urine tests showed a 53% (OR = 0.47, 95% CI 0.23–0.97), 56% (OR = 0.44, 95% CI 0.21–0.93), and 66% (OR = 0.34, 95% CI 0.13–0.89) reduction in the risk of being stone-free at 7 days. At 2 months, the reductions were 72% (OR = 0.28, 95% CI 0.12–0.67), 74% (OR = 0.26, 95% CI 0.11–0.65), and 76% (OR = 0.24, 95% CI 0.08–0.71). This indicates that the presence of preoperative urinary tract infections may reduce the stone discharge rate as well as increase the likelihood of adhesions and obstructions.

A comparison of surgical complications between the PCNL group (n = 12) and NP-URL-FU group (n = 16) is shown in Supplementary Fig. 1 and Supplementary Table 1. The most common complication observed was fever within the first 3 days postoperatively. In the NP-URL-FU group, 14 patients (87.5%) experienced this complication compared to 10 patients (83.3%) in the PCNL group, with no statistically significant difference between the two groups (p = 0.550). Perirenal hematoma occurred in 2 patients (16.7%) in the PCNL group, while no cases were reported in the NP-URL-FU group (p = 0.242). Ureteral injury was observed in 2 patients (12.5%) in the NP-URL-FU group, while no such injuries were noted in the PCNL group (p = 0.497). Although the rates of complications varied between the two groups, none of the differences reached statistical significance.