CRC patients who underwent radical surgery were included from Jan 2011 to Jan 2020 in a single clinical teaching hospital. This study was performed following the World Medical Association Declaration of Helsinki. And this study obtained Ethical approval from the institutional review board (The First Affiliated Hospital of Chongqing Medical University, 2024–010-01). All patients participating in the study obtained written informed consent.

Patients who underwent primary CRC surgery were included in this study (n=5473). The exclusion criteria were as follows: 1, patients with incomplete clinical information (n=323); 2, non-R0 surgery (n=25); 3, stage IV CRC (n=875); and 4, incomplete renal function examination (n=194). Finally, a total of 4056 patients were included in this study. The flowchart and inclusion and exclusion criteria were shown in Figure 1 .

All included patients underwent total mesorectal resection or total mesocolic resection based on the oncological principles, with postoperative pathology confirming R0 resection. Routine follow-up was performed after surgery: every three months for three years, and every six months thereafter.

We used the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) creatinine equation to calculate eGFR to assess renal function in all the included patients. The CKD-EPI equation was gender-specific, and the specific formula was as follows: eGFR = 141 × min (Scr/κ, 1)α × max (Scr/κ, 1)- 1.209× 0.993 Age× 1.018 [if female], where Scr was serum creatinine, κ was 0.7 for females and 0.9 for males, α was −0.329 for females and −0.411 for males, min indicated the minimum of Scr/κ or 1, and max indicated the maximum of Scr/κ or 1 (16, 17). CKD was defined as persistent proteinuria or eGFR<60ml/min/1.73m² (18), therefore, we defined patients with eGFR< 60ml/min/1.73m² as the CKD group and those with eGFR≥ 60ml/min/1.73m² as the Non-CKD group. The pathological staging of tumors was basically based on the AJCC 8th edition diagnosis (19). Complications were defined according to the Clavien- Dindo classification (20) and major complications were defined as Clavien- Dindo classification ≥ III complications. III Complications Includes complications requiring surgical, endoscopic, or radiologic intervention; OS was defined as the time from the date of surgery to the individual patients’ death of any cause or the last follow-up time; DFS was defined as the time from the date of surgery to the date of radiographic or pathological confirmation of recurrence, death or the last follow-up.

We retrospectively collected baseline information and postoperative short-term outcomes through the inpatient system. Baseline information included age, gender, body mass index (BMI), smoking and drinking history, hypertension, type 2 diabetes mellitus (T2DM), tumor location, tumor size and tumor stage ( Table 1 ). Postoperative short-term outcomes included operative time, blood loss, hospital stay, overall complications and major complications ( Table 2 ). Survival data were mainly obtained through the outpatient follow-up system and telephone interviews.

Since the grouping of the CKD group and the Non-CKD group was non-random, and variables were unbalanced. Therefore, we used PSM in this study. Propensity scores are most commonly estimated by logistic regression, where treatment group is considered the outcome and regressed against observed baseline characteristics (21). We initiated a 1:1 (CKD group vs Non-CKD group) matching analysis by PSM and nearest neighbor matching algorithms and specified a caliper width with 0.01 standard deviation to adjust for differences in baseline characteristics between the two groups. Baseline information for PSM included age, gender, BMI, smoking and drinking history, hypertension, T2DM, tumor location, tumor size and tumor stage.

In this article, continuous variables were expressed as mean ± SD, and Frequency variables were expressed as n (%). We use independent samples t-test to analyze differences in eGFR, age, BMI, operation time, blood loss and hospital stay between the CKD group and the Non-CKD group. The chi-square test or Fisher’s exact test was used to analyze differences in sex, smoking, drinking, hypertension, T2DM, tumor location, tumor size, tumor stage, overall complications and major complication between the CKD group and the Non-CKD group. Furthermore, to identify independent predictors of OS and DFS, we used the Cox regression analysis. Firstly, we performed univariate analysis for CKD, Sex, BMI, T2DM, Tumor site, Tumor stage, Smokin, Drinking, Hypertension, Tumor size, Overall complications in the two groups, and then multivariate analysis for factors with P-value <0.05 after univariate analysis. Data were analyzed using the SPSS (version 26.0) statistical software, and a bilateral p-value < 0.05 was considered statistically significant.

According to the relevant inclusion and exclusion criteria, a total of 4056 patients undergoing CRC surgery were finally included in this analysis, including 723 patients in the CKD group and 3333 patients in the Non-CKD group. After 1:1 PSM, there were 666 patients in each group ( Figure 1 )

Before PSM, there were significant differences in the baseline information between the CKD group and the Non-CKD group. The CKD group had older age (P<0.01), a higher proportion of male (P<0.01), higher BMI (P=0.013), higher proportions of smoking and drinking (P<0.01), and more patients with hypertension and T2DM (P<0.01). After 1:1 PSM, there was no significant difference in baseline information between the two groups (p>0.05) ( Table 1 )

Compared the short-term postoperative outcomes between the CKD group and the Non-CKD group, we found that the CKD group had more blood loss (P=0.025), longer postoperative hospital stay (P<0.01), more overall complications (P<0.01) and more major complications (P=0.003). After PSM, the CKD group still had a longer postoperative hospital stay (P=0.009) and a higher incidence of overall complications (p=0.050). CKD might not affect major complications (P=0.358) ( Table 2 ).

This study counted the postoperative complications with higher morbidity, such as intestinal obstruction, lymphatic fistula, anastomotic fistula, thrombus, postoperative death and pneumonia. Before PSM, the incidence of intestinal obstruction, lymphatic fistula, anastomotic fistula, thrombus, postoperative death and pneumonia in the CKD group was 2.4%, 0.3%, 2.5%, 1.9%, 0.7%, and 6.4%, respectively. The incidence of intestinal obstruction, lymphatic fistula, anastomotic fistula, thrombus, postoperative death and pneumonia in the Non-CKD group was 1.8%, 0.5%, 2.3%, 0.8%, 0.2%, and 2.3%, respectively. After PSM, the incidence of intestinal obstruction, lymphatic fistula, anastomotic fistula, thrombus, postoperative death and pneumonia in the CKD group was 2.6%, 0.3%, 2.6%, 2.0%, 0.7%, 5.6%, respectively. The incidence of intestinal obstruction, lymphatic fistula, anastomotic fistula, thrombus, postoperative death and pneumonia in the Non-CKD group was 2.9%, 0.7%, 3.6%, 0.7%, 0.2%, 4.8%, respectively.

The median follow-up time was 33 (1–114) months. Before PSM, in terms of OS, age (p<0.01, HR=1.039, 95% CI=1.031–1.048), tumor stage (p<0.01, HR=2.094, 95% CI=1.827–2.401, tumor size (p=0.005, HR=1.275, 95% CI=1.075–1.511) and overall complications (p<0.01, HR=1.664, 95% CI=1.391–1.990) were independent predictors. Regarding DFS, age (p<0.01, HR=1.028, 95% CI=1.020–1.035), tumor stage (p<0.01, HR=2.022, 95% CI=1.792–2.281), and overall complications (p<0.01, HR=1.532, 95% CI=1.300–1.805) were independent predictors. However, CKD was not an independent predictor of OS or DFS (OS: p=0.440, HR=1.085, 95% CI=0.882–1.335); DFS: p=0.122, HR=1.160, 95% CI=0.961–1.399) ( Table 3 ).

After PSM, in terms of OS, age (p<0.01, HR=1.045, 95% CI=1.028–1.062), tumor stage (p<0.01, HR=1.931, 95% CI=1.564–2.385) and overall complications (p<0.01, HR=1.858, 95% CI=1.423–2.425) were independent predictors. Regarding DFS, age (p<0.01, HR=1.034, 95% CI=1.020–1.049), tumor stage (p<0.01, HR=1.852, 95% CI=1.537–2.231), and overall complications (p<0.01, HR=1.651, 95% CI=1.295–2.10) were independent predictors. However, CKD was not an independent predictor of OS or DFS (OS: p=0.619, HR=1.070, 95% CI=0.820–1.396; DFS: p=0.472, HR=1.092, 95% CI=0.859–1.389) ( Table 4 ).