A comparative study on outcomes of ABO-incompatible kidney transplants between robot-assisted vs. open surgery-propensity score-matched analysis: a retrospective cohort study

Abstract

Background

Robot-assisted kidney transplantation (RAKT) is increasingly being adopted worldwide. Despite this growing interest, there remains a notable gap in the literature, especially concerning its effectiveness in immunologically high-risk patients compared to conventional open kidney transplantation (OKT). This study investigates the viability and success of RAKT in comparison with OKT, particularly for recipients with ABO incompatibility (ABOi).

Methods

This retrospective, single-center study included 239 living-donor transplants between October 2020 and February 2023, with 210 patients undergoing ABOi-OKT and 29 undergoing ABOi-RAKT. A composite of biopsy-proven acute rejection (BPAR), graft failure, and the development of de novo donor-specific antibodies was analyzed through univariate and multivariate models. Propensity score matching (PSM) was utilized to ensure a balanced comparison between the two groups. Following PSM, a total of 131 cases in the OKT group and 26 cases in the RAKT group were analyzed.

Results

After PSM, the mean recipient age was 48.56 years for OKT and 47.96 years for RAKT. Both groups had comparable one-year (RAKT: 92.4%, OKT: 93.1%) and two-year BPAR-free survival rates (RAKT: 92.4%, OKT: 91.9%). Mean estimated glomerular filtration rate values were similar at 12 months post-transplant (RAKT: 62.15 ml/min/1.73 m², OKT: 64.53 ml/min/1.73 m²). Operative times were significantly longer for RAKT (291.42 vs. 150.81 min, p < 0.001), while cold ischemic time was also longer for RAKT (119.77 vs. 47.22 min, p < 0.001). Hospital stays were shorter for RAKT (median 6 vs. 8 days, p < 0.001). There was no significant difference in the composite outcome of BPAR, graft failure, and de novo donor-specific antibodies between the two groups (HR 0.858, 95% CI: 0.180–4.096, p = 0.848).

Conclusions

RAKT is a safe and effective alternative to OKT in ABOi patients, demonstrating similar perioperative outcomes, graft survival rates, and renal function. The application of ropensity score matching analysis strengthens the reliability of these findings, confirming RAKT’s viability for high-risk kidney transplant recipients.

Trial registration

The clinical trial associated with this study was registered on 2024-02-24 with the Clinical Trial Number NCT06287008||https://www.clinicaltrials.gov/)

Background

Kidney transplantation (KT) has become the preferred treatment for end-stage renal disease (ESRD), offering patients enhanced survival, better quality of life, and independence from dialysis maintenance [1,2,3]. The increasing incidence of ESRD has led to a heightened demand for donor kidneys, while their availability remains scarce. This disparity has resulted in extended waiting periods for those in need of KT. To mitigate this shortage, various strategies have been developed, including significant advancements in desensitization protocols. These protocols have effectively overcome immunological challenges, facilitating transplants across human leukocyte antigen (HLA) and ABO blood group incompatibilities.

Historically, ABO incompatibility was considered a definitive barrier to KT due to the high risk of hyperacute rejection and poorer outcomes stemming from blood type mismatches [4]. Recent advances in immunosuppressive therapies and desensitization techniques, however, have enabled successful ABO-incompatible (ABOi) KT globally. As a result, ABOi KT is now widely recognized as a feasible option for ESRD treatment, yielding outcomes on par with ABO-compatible (ABOc) KT in both adults and children [5,6,7].

Robot-assisted kidney transplantation (RAKT) has seen impressive progress since its first successful procedure in France in 2001 [8]. This innovative method has transformed KT, offering superior precision, enhanced visualization, and benefits for surgeons and recipients alike. However, the application of RAKT in immunologically high-risk patients is less documented, and detailed studies comparing RAKT with traditional open KT (OKT) in these scenarios are essential to evaluate the feasibility and advantages of the robotic method.

In a preliminary study by T. Prudhomme et al., the perioperative outcomes of ABOi-RAKT, ABOc-RAKT, and ABOi-OKT were examined in obese patients. The study highlighted the benefits of RAKT for this group, such as improved surgical visibility, lower infection rates, reduced wound complications, and less lymphocele formation compared to OKT. The findings indicated no significant difference in kidney graft survival rates two years post-transplant between the ABOi-RAKT and ABOi-OKT groups [9].

To fully assess the safety and efficacy of RAKT in ABOi-KT, it is crucial to extend research beyond obese patients and include a broader patient demographic. Thus, our current study aims to compare perioperative and graft outcomes between ABOi-RAKT and ABOi-OKT across a more diverse patient population. To ensure a robust comparison, we employed propensity score matching (PSM) analysis, which allowed us to account for various recipient and donor characteristics, immunosuppressant usage, and operative details. This method will provide a balanced comparison between the two groups, enhancing the reliability of our findings and contributing to a comprehensive evaluation of the perioperative and graft outcomes associated with these surgical techniques.

Methods

Study patients

This retrospective, single-center study encompassed 210 patients who underwent ABOi-OKT and 29 who underwent ABOi-RAKT between October 2020 and February 2023. All RAKT procedures were performed by the same surgeon, while the OKT procedures were carried out by a team of experienced surgeons at our center. Notably, all transplants in this study were from living donors.

Prior to surgery, recipients underwent preoperative computed tomography to evaluate their vascular anatomy and detect potential atherosclerosis in the iliac vessels, critical for vascular anastomosis. Our center adhered to stringent protocols for preoperative donor evaluation, immunosuppressant regimens, postoperative care, and follow-up.

The study was approved by the ethics committee at our institution (reference number: 2023-0085). Owing to the retrospective nature of the study, the requirement for informed consent was waived.

We followed the STROBE statement and this study is fully compliant with the STROCSS criteria [10].

Desensitization protocol

Our prior publications [11,12,13] provide a comprehensive overview of the desensitization procedures we have developed for managing ABO incompatibilities. These include using rituximab, an anti-CD20 monoclonal antibody, and therapeutic plasma exchange (TPE) to lower antibody levels. ABOi recipients receive a single dose of rituximab (100–200 mg) one week before starting TPE, which continues until immunoglobulin M (IgM) isoagglutinin levels are safely reduced to ≤ 1:4, and for blood type O recipients, IgG levels are also reduced to ≤ 1:16. If there is a rebound in isoagglutinin levels, reaching or exceeding a titer of 1:16, postoperative TPE is considered.

Surgical techniques of RAKT

In our earlier publication [14], we have provided a thorough description of the surgical technique and the instruments used for RAKT. In brief, during the surgical procedure for RAKT, the patient was positioned at a 45-degree angle in the Trendelenburg position and securely fastened to the operating table. The initial steps involved exposing the iliac vessels and creating an extraperitoneal pouch, followed by the separation of the bladder to prepare for the ureteroneocystostomy. The graft, enclosed in a gauze jacket, was introduced into the abdominal cavity through the GelPOINT device. Regional hypothermia was induced by applying 200 to 250 cc of ice slush to cool the graft via the GelPOINT. Subsequently, a venotomy was made with Potts scissors, and the renal vein of the graft was joined to the external iliac vein in a continuous end-to-side manner. The external iliac artery was clamped, and an arteriotomy was created using robotic Potts scissors and the clamped artery was washed with heparinized saline. The renal artery was then connected to the external iliac artery in an end-to-side continuous manner. Once the anastomosis was confirmed to be secure, the blood supply to the kidney was restored and assessed for color and turgor. Throughout the entire anastomosis procedure, the pneumoperitoneum was reduced to 8 mm Hg to facilitate the detection of any bleeding. Following this, the kidney was placed into the extraperitoneal pouch, and the ureterovesical anastomosis was performed using a modified Lich-Gregoir technique. This involved creating two semi-continuous sutures with 4 − 0 Monocryl sutures over a previously inserted 6 F, 14 cm Double-J stent. Finally, the detrusor muscle was closed using a continuous suture to establish an anti-reflux mechanism.

Clinical outcomes

We retrospectively reviewed patient records to collect clinical data. The primary endpoint was biopsy-proven acute rejection (BPAR). Allograft biopsies were evaluated based on Banff 2015 [15] and Banff 2017 criteria [16]. Graft survival was defined as the time from KT to graft removal or the resumption of dialysis. We included composite outcomes in our analysis, comprising BPAR, graft failure, and de novo donor-specific antibody (DSA) occurrences.

Kidney graft function was assessed by measuring the estimated glomerular filtration rate (eGFR) for up to one year post-KT, calculated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation [17].

Statistical analysis

To ensure appropriate statistical comparisons, categorical variables were analyzed using the χ2 test or Fisher’s exact test, depending on the sample size. Continuous variables were examined using the Student’s t-test or Wilcoxon rank-sum test, based on their distribution.

Rejection-free survival rates were analyzed using Kaplan-Meier curves and the log-rank test. Univariate and multivariate analyses using the Cox proportional hazards method were conducted to identify factors influencing graft survival and rejection events prior to PSM.

We employed PSM to ensure a balanced comparison between the outcomes of the two groups. The covariates used in PSM included recipient age, recipient sex, recipient BMI, hemodialysis type, months on hemodialysis before transplantation, number of retransplant patients, ABDR mismatch, HLA incompatibility in KT, desensitization with Rituximab, IgM titer, donor-specific antibody, induction therapy, calcineurin inhibitor, donor age, donor sex, donor BMI, relationship with donor, donor diabetes mellitus, donor hypertension (HTN), donor 24-hour creatinine clearance, donor 24-hour proteinuria, and the side of the kidney transplanted. The matching process utilized the nearest neighbor method with a caliper of 0.3, performed without replacement, and a matching ratio of 7:1. The primary outcome was evaluated using a stratified Cox proportional hazards model to determine the effect of the transplantation methods on the risk of biopsy-proven acute rejection (BPAR), accounting for the correlated nature of matched pairs. Secondary outcomes, such as estimated glomerular filtration rate (eGFR) at various time points and were analyzed using linear mixed-effects models, which considered the random effects of the matched pairs (subclass) as well as occurrences of infectious complications using a forest plot anlaysis after PSM.

The risk reduction shown in the forest plot is expressed as risk difference values. This forest plot was generated to emphasize the comparative outcomes between the two study groups. The 95% confidence intervals for these risk differences were determined using the Wald-type confidence interval.

Statistical significance was set at a p-value of less than 0.05. All analyses were performed using IBM SPSS version 22.0 (IBM Corp., Armonk, NY, USA).

Results

Baseline characteristics of study population

Table 1 presents a comprehensive comparison of various recipient, donor, immunosuppressant, and operative variables between OKT and RAKT both before and after PSM. Before matching, the mean ages of recipients were 50.51 years for the OKT group and 47.17 years for the RAKT group (p = 0.154, SMD = 0.3256). After matching, the mean ages were 48.56 years (OKT) and 47.96 years (RAKT) (p = 0.810, SMD = 0.0063). Gender distribution was 46.19% females (OKT) and 41.38% (RAKT) before matching (p = 0.626, SMD = 0.0977), and 48.9% vs. 42.3% after matching (p = 0.692, SMD = 0.0911). BMI averaged 23.24 kg/m² (OKT) and 24.23 kg/m² (RAKT) before matching (p = 0.300, SMD = 0.2038), and 23.66 kg/m² vs. 24.16 kg/m² after matching (p = 0.580, SMD = 0.0144). Dialysis duration showed a significant initial difference with medians of 5 months (OKT) vs. 1 month (RAKT) (p = 0.021, SMD = 0.1572), which reduced to 4 months vs. 1.5 months after matching (p = 0.152, SMD = 0.0225). Retransplantation rates were 8.57% (OKT) and 0% (RAKT) before matching (p = 0.140, SMD = 0.326), with alignment after matching. The number of HLA mismatches was similar between OKT and RAKT before matching, with a median of 4 (range 3–5) in both groups (p = 0.993, SMD = 0.0081). After matching, the median remained 4 (range 3–5) in the OKT group and 3 (range 3–5) in the RAKT group, with no significant difference (p = 0.705, SMD = 0.0992). IgM titer levels were comparable between the groups before matching (median 64, range 32–128 in OKT vs. median 32, range 16–64 in RAKT, p = 0.094, SMD = 0.9886) and after matching (median 64, range 32–128 in OKT vs. median 32, range 16–64 in RAKT, p = 0.209, SMD = 0.1660). The causes of ESRD were analyzed between patients undergoing OKT and RAKT before PSM. HTN caused ESRD in 9.5% of OKT patients and 10.3% of RAKT patients, while diabetes mellitus (DM) was more frequent in RAKT (34.5%) than in OKT (28.6%). Glomerulonephritis (GN) accounted for 9.5% of OKT cases and 13.8% in RAKT. IgA nephropathy was found in 18.6% of OKT and 20.7% of RAKT patients. Focal segmental glomerulosclerosis (FSGS) occurred in 2.9% of OKT and 3.5% of RAKT patients. Polycystic kidney disease (PCKD) was seen in 7.1% of OKT cases but absent in RAKT. Other causes such as Alport’s syndrome, systemic lupus nephritis, congetinal renal agenesis, nephronophthisis, obstructive uropathy, reflux nephropathy and horseshoe kidney accounted for 6.2% of OKT and 6.9% of RAKT cases. Overall, the distribution of causes of ESRD between OKT and RAKT patients did not show statistically significant differences (p = 0.763).

Table 1 Baseline characteristics before and after propensity score matching

The use of induction agents like basiliximab and thymoglobulin showed no significant difference before (p = 0.795, SMD = 0.0971) and after matching (p = 1, SMD = 0.0765), with 82.86% of OKT recipients and 86.21% of RAKT recipients initially receiving basiliximab, and 85.5% vs. 84.6% after matching. Calcineurin inhibitor use, mainly tacrolimus, was consistent before (p = 0.479, SMD = 0.0846) and after matching (p = 1, SMD = 0.0527), with nearly all recipients treated with tacrolimus (98.1% OKT vs. 96.55% RAKT before; 97.7% OKT vs. 96.2% RAKT after).

Donor mean age was 51.02 years for OKT and 49.14 years for RAKT before matching (p = 0.401, SMD = 0.1453), and 49.9 vs. 50 years after matching (p = 0.968, SMD = 0.0281). Gender distribution was 58.57% females (OKT) and 68.97% (RAKT) before matching (p = 0.285, SMD = 0.2247), and 56.5% vs. 65.4% after matching (p = 0.534, SMD = 0.0758). Donor BMI showed no significant difference before (24.40 kg/m² OKT vs. 23.89 kg/m² RAKT, p = 0.424, SMD = 0.1329) and after matching (24.23 kg/m² vs. 23.89 kg/m², p = 0.637, SMD = 0.0452). Other donor characteristics, including DM, HTN, and renal function (24-hour creatinine clearance and proteinuria), were balanced before and after matching.

Perioperative outcomes

Operative times were significantly longer for RAKT recipients (Table 1). Before matching, cold ischemic time was 48.57 min for OKT vs. 116.83 min for RAKT (p < 0.0001), and 47.22 min vs. 119.77 min after matching (p < 0.001). Anastomosis and total operative times were also longer for RAKT both before (21.09 vs. 45.41 min for anastomosis, p < 0.0001; 152.91 vs. 296.83 min for operative time, p < 0.0001) and after matching (29.49 vs. 45.35 min for anastomosis, p < 0.001; 150.81 vs. 291.42 min for operative time, p < 0.001). Hospitalization was shorter for RAKT recipients both before (median 6 days vs. 8 days, p < 0.0001) and after matching (median 6 days vs. 8 days, p < 0.001). Post-transplant renal function, measured by eGFR (CKD-EPI) one month after KT, was similar between the groups (68.23 ml/min/1.73 m² in OKT vs. 71.28 ml/min/1.73 m² in RAKT before matching, p = 0.426; 68.57 vs. 71.81 ml/min/1.73 m² after matching, p = 0.439). Notably, there were no cases of delayed graft function (DGF) observed in either the RAKT or OKT groups.

Univariate and multivariate analysis for a composite of BPAR, graft failure, and de novo DSA

In the univariate analysis with a composite outcome of BPAR, graft failure, and de novo DSA, the type of surgery did not significantly affect the composite outcome (Table 2). However, HLA-incompatible kidney transplants were significantly associated with the outcome, demonstrating a hazard ratio (HR) of 3.75 (95% CI: 1.744–8.074, p = 0.0007). The multivariable analysis indicates that this association might be significant, with an HR of 2.889 (95% CI: 0.974–8.564, p = 0.0557), suggesting a potential differential impact of HLA incompatibility across transplant groups. Pre-transplant DSA also displayed a significant association in the univariate analysis (HR 3.092, 95% CI: 1.475–6.482, p = 0.0028), but this significance was not maintained in the multivariate analysis (HR 2.161, 95% CI: 0.842–5.547, p = 0.1091). Additionally, thymoglobulin induction was significantly associated with the composite outcome in the univariate analysis (HR 2.527, 95% CI: 1.15–5.553, p = 0.021), but this association was not significant in the multivariate analysis, indicating that thymoglobulin’s effect might be influenced by additional variables. Lastly, no donor factors showed significant association with the composite outcome. Overall, these analyses suggest that factors such as HLA incompatibility and pre-transplant DSA have significant associations in univariate contexts, but their impacts become more nuanced in multivariate analyses.

Table 2 Univariate and multivariate analysis of factors associated with a composite of graft failure, BPAR and de novo DSA

Comparison of biopsy-proven acute rejection-free graft survival and renal function between RAKT and OKT recipients

To compare BPAR-free graft survival between RAKT and OKT recipients, Kaplan-Meier curves were used (Fig. 1). Both groups showed similar BPAR-free graft survival rates over the observation period. The RAKT group had a BPAR-free survival rate of 92.4% at 1 and 2 years, while the OKT group had rates of 93.1% at 1 year and 91.9% at 2 years, with no statistically significant difference (p = 0.99).

Fig. 1

Kaplan-Meir survival curve for biopsy-proven acute rejection free graft survival

We performed a PSM analysis to further assess the impact of RAKT versus OKT on BPAR-free survival and composite outcomes, including recipient and donor characteristics, immunosuppressant usage, and operative details for balanced comparisons.

Table 3 shows the adjusted relative hazard for BPAR-free survival and composite outcomes in both groups, before and after PSM. Initially, the hazard ratio (HR) for BPAR-free survival in the RAKT group compared to the OKT group was 1.007 (95% CI: 0.229, 4.431, p = 0.993), indicating no significant difference. After PSM, the HR for BPAR-free survival in the RAKT group was 0.858 (95% CI: 0.180, 4.096, p = 0.848), suggesting no significant difference between RAKT and OKT in terms of BPAR-free survival when matched for relevant covariates.

Table 3 The adjusted relative hazard for BPAR-free survival and composite graft failure in robot-assisted versus open surgery for ABO-incompatible kidney transplants

For the composite outcome of graft failure, BPAR, and de novo DSA-free survival, the HR for the RAKT group in the original unadjusted data was 0.982 (95% CI: 0.224, 4.307, p = 0.981), showing no significant difference. After matching, the HR was 0.858 (95% CI: 0.180, 4.096, p = 0.848), still indicating no significant difference between RAKT and OKT. These PSM results confirm that the risks of BPAR-free survival and composite outcomes are comparable between the groups, supporting the equivalence of these surgical techniques in post-transplant outcomes.

Figure 2 shows the overall trend in eGFR values determined via the CKD-EPI Creatinine Equation, with similar patterns between RAKT and OKT groups (p = 0.20). The mean eGFR values were 62.15 ml/min/1.73 m² for the RAKT group and 64.53 ml/min/1.73 m² for the OKT group.

Fig. 2

Trends of eGFR values over follow-up periods up to 1 year after transplantation in matched cohort

Table 4 provides a detailed comparison of post-transplant eGFR values at various time points between OKT and RAKT recipients before and after PSM. Before matching, the mean eGFR at discharge was 76.40 (± 20.79) ml/min/1.73 m² for OKT and 74.48 (± 18.91) ml/min/1.73 m² for RAKT (p = 0.638). At 1 month post-transplant, the mean eGFR values were 68.23 (± 19.55) ml/min/1.73 m² for OKT and 71.28 (± 16.95) ml/min/1.73 m² for RAKT (p = 0.426). At 6 months, the values were 62.91 (± 17.44) ml/min/1.73 m² for OKT and 62.03 (± 17.26) ml/min/1.73 m² for RAKT (p = 0.799). At 12 months, the mean eGFR values were 64.17 (± 19.61) ml/min/1.73 m² for OKT and 62.38 (± 14.85) ml/min/1.73 m² for RAKT (p = 0.636).

Table 4 Comparison of post-transplant estimated glomerular filtration rate (CKD-EPI) at various time points between OKT and RAKT before and after propensity score matching

After matching, the comparison remained consistent with no significant differences observed. At discharge, the mean eGFR was 74.50 (± 20.93) ml/min/1.73 m² for OKT and 74.12 (± 18.50) ml/min/1.73 m² for RAKT (p = 0.931). At 1 month, the mean eGFR was 68.57 (± 19.80) ml/min/1.73 m² for OKT and 71.81 (± 17.41) ml/min/1.73 m² for RAKT (p = 0.440). At 6 months, the values were 63.09 (± 18.37) ml/min/1.73 m² for OKT and 61.58 (± 18.15) ml/min/1.73 m² for RAKT (p = 0.701). At 12 months, the mean eGFR was 64.53 (± 20.01) ml/min/1.73 m² for OKT and 62.15 (± 15.33) ml/min/1.73 m² for RAKT (p = 0.568).

Infectious complications

We also performed a comparative analysis of the etiologies behind post-transplant infections necessitating hospital admission (see Additional Data 1 for details). For urinary tract infections, the OKT group had diverse organisms: E. coli (9.5%), K. pneumoniae (5.2%), Klebsiella aerogenes (2.4%), Enterococci (3.3%), and Proteus mirabilis (1%). The RAKT group had lower incidences: E. coli (6.9%) and K. pneumoniae (13.8%). Pneumonia from Covid-19 was noted in 2.4% of the OKT group. Cytomegalovirus syndrome was exclusive to the OKT group (1.4%). Bacteremia in the OKT group included E. coli (2.4%) and Bacteroides fragilis (0.5%); in the RAKT group, E. coli and K. pneumoniae (3.4%, each). Postoperative infections in the OKT group involved various organisms, including K. pneumoniae, Streptococcus parasanguinis, Staphylococcus aureus, Enterococcus faecalis, E. coli, B. fragilis, and Candida albicans (0.5–1% each). Fungal infections (candidiasis) were found in 1% of the OKT group. Gastrointestinal infections in the OKT group included Sapovirus (0.5%) and Clostridium difficile (1%).

The forest plot in Fig. 3 illustrated the risk reduction for various infections with RAKT compared to Open KT. For urinary tract infections, the risk reduction was − 2.12% (95% CI: -17.77, 13.54). Pneumonia had a risk reduction of 2.38% (95% CI: 0.32, 4.44), viral infections 1.43% (95% CI: -0.18, 3.03), and bacteremia of unknown origin − 0.59% (95% CI: -7.60, 6.42). Postsurgical and fungal infections had risk reductions of 0.84% (95% CI: -6.35, 8.02) and 0.95% (95% CI: -0.36, 2.27) respectively. Gastrointestinal infections had a risk reduction of 1.43% (95% CI: -0.18, 3.03). None of these differences were statistically significant, indicating that RAKT does not substantially change the risk of postoperative infections compared to OKT.

Fig. 3

Forest plot showing risk reduction in infectious complications for RAKT compared to OKT

Discussion

Multiple studies have explored the feasibility, safety, and appropriateness of RAKT in ESRD patients [8, 18,19,20,21,22,23]. Initially, research on RAKT primarily focused on its technical aspects, often overlooking comprehensive clinical outcome data. However, as RAKT’s adoption increased, a richer dataset emerged, enhancing our understanding of its clinical outcomes and allowing for direct comparisons with traditional open methods.

A range of studies has investigated the functional results and associated risks of both RAKT and OKT. For instance, research by J. Oberholzer and colleagues focused on the effectiveness of RAKT in obese patients, traditionally considered unsuitable for transplantation due to high BMIs averaging 42.6 ± 7.8 kg/m². Comparing these patients with a similar cohort undergoing OKT, they found that renal function, measured by serum creatinine levels six months post-transplant, was similar in both groups (1.5 mg/dL ± 0.4 for RAKT vs. 1.6 mg/dL ± 0.6 for OKT, p = 0.47). Despite the six-month follow-up limitation, other metrics like graft survival, patient survival, rejection rates, and infection frequencies were comparable [20].

Additionally, a study by Volkan T. compared 40 RAKT and 40 OKT cases performed by the same surgeon [24]. The results indicated similar functional outcomes in both groups, with creatinine levels at six months post-transplantation being 0.95 ± 0.90 mg/dL for RAKT and 0.87 ± 0.73 mg/dL for OKT (p = 0.638). A recent systematic analysis also found no significant differences in patient and graft survival across various KT methods (open, laparoscopic, robotic) [25].

While existing literature focuses on immunologically compatible patients, there’s a gap in research exploring the impact of immunological risk on RAKT vs. OKT outcomes. T. Prudhomme and colleagues studied ABOi-RAKT in overweight patients, contrasting with ABOi-OKT. They observed longer cold ischemia times, operation durations, and rewarming intervals in the ABOi-OKT group (p < 0.001). Additionally, the ABOi-RAKT group showed a 0% rate of DGF, compared to 10.7% in ABOi-OKT (p = 0.60), with similar graft survival rates observed in both groups [9].

Our research fills a gap by comparing clinical outcomes between ABOi-RAKT and ABOi-OKT in a broader demographic, not limited to overweight patients. The analysis of BPAR-free survival and composite outcome further supports the equivalence of RAKT and OKT. Our findings indicate no significant difference in BPAR-free survival rates between the two groups, both before and after propensity score matching. Additionally, the composite outcome of graft failure, BPAR, and de novo DSA-free survival did not differ significantly between RAKT and OKT, suggesting similar effectiveness in preventing these adverse outcomes.

Moreover, the comparison of post-transplant eGFR values at various time points showed no significant differences between the OKT and RAKT groups. This consistency in renal function outcomes across multiple post-transplant periods reinforces the conclusion that the surgical technique—whether robot-assisted or open—does not significantly impact the efficacy of kidney transplantation. These results collectively demonstrate that RAKT is a viable and comparable alternative to OKT in terms of both graft survival and renal function post-transplant.

Some prior studies have reported varied results regarding whether ABOi KT increases infectious complications. Several studies have indicated a heightened risk of postoperative infections in ABOi-KT patients, attributed to the more intensive immunosuppression and the need for pretransplant desensitization procedures such as plasmapheresis or immunoadsorption therapies [26,27,28]. The intensified immunosuppression protocols and desensitization measures elevate the risk of infections in these patients [29, 30]. Habicht et al. found an increased risk of infectious complications, particularly viral infections, in ABOi patients [26]. Similarly, Lentine et al. noted a higher risk of pneumonia and urinary tract infections within the first 90 days post-transplant, and a higher risk of wound infections from 91 to 365 days post-transplant in ABOi recipients [27]. Conversely, Kakuta et al., Zschiedrich et al., and Hamano et al. did not observe a higher risk of infectious complications in ABOi-KT recipients [31,32,33].

Moreover, there is a scarcity of published studies that have conducted comparative analyses of infectious complications in the context of surgical contexts between robot-assisted and open techniques. A systematic review comparing perioperative outcomes in RAKT versus OKT found that the rate of surgical site complications, primarily infections, was lower in the RAKT group [34]. This anticipated outcome is attributed to the inherent benefits of RAKT, such as smaller incision sites compared to OKT. The minimally invasive approach of RAKT minimizes the exposure of internal tissues to external contaminants, thereby reducing the risk of infection. Smaller incisions also promote quicker healing and decrease the overall incidence of post-operative complications like wound infections.

To the best of the author’s knowledge, no studies have specifically addressed the issue of infectious complications between RAKT and OKT in ABOi cases. Our study is the first to show that the surgical technique, whether robot-assisted or open, does not lead to an increase in infectious complications. This finding is significant as it supports the safety of RAKT in terms of infectious risk, demonstrating that the choice of surgical approach does not significantly affect the incidence of postoperative infections in ABOi KT patients.

Study limitations

Our study had several limitations. As a single-center retrospective study with unequal participant numbers, it may have limited statistical power and potential biases. The imbalance in group sizes, influenced by non-random factors, could introduce additional biases. We used propensity score matching to address sample size differences, enhancing the reliability of our findings, but these limitations should still be considered. Another constraint is the limited timeframe for outcome assessment due to the recent initiation of RAKT at our center. While short-term results are promising, longer-term research is needed. Additionally, the selection of ABOi patients occurred before the robotic surgical learning curve was fully optimized, which may have contributed to prolonged cold ischemia and surgery times. Future studies focusing on this group after the learning curve has been improved would provide more accurate insights.

Conclusion

The findings from this study demonstrate that RAKT and OKT provide comparable outcomes in terms of BPAR-free survival, composite outcome of graft failure, BPAR, and de novo DSA, and post-transplant renal function. The propensity score matching effectively balanced the baseline characteristics between the two groups, ensuring a robust comparison. Despite longer operative times, RAKT recipients experienced shorter hospital stays, suggesting potential advantages in recovery. These results support the use of robot-assisted techniques in kidney transplantation, offering an alternative approach without compromising patient outcomes. Future research should aim for more comprehensive studies with longer follow-up to solidify these initial findings.