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Residual renal volume as a long-term independent predictive factor of developing chronic kidney disease after donor nephrectomy – Scientific Reports

In our research, we examined the long-term renal function in kidney donors. We identified that gender, age, and greater remaining renal volume independently contribute to the risk of developing chronic kidney disease (CKD) following both open and laparoscopic donor nephrectomy procedures. Our results contradicted those reported in previous studies with differing follow-up durations17,18. Hori et al. and Lange et al. both proposed a correlation between kidney volume and kidney function before and after donation. Additionally, Narasimhamurthy et al. indicated that kidney size is linked to the long-term eGFR. In fact, one study has indicated a robust correlation between the volume of the renal cortex and eGFR after kidney donation19. The total parenchymal renal volume contouring (ReRCoV) method has demonstrated the most substantial predictive efficacy for the development of chronic kidney disease (CKD) one year after kidney donation, as per previous research20.

Our results indicate that higher residual renal volume is associated with developing CKD in long-term follow-up, which contradicted previous studies. Meta-analysis by Habbous et al. might help clarify the inconsistencies, as they discovered that the apparent link between renal volume and post-donation renal function was notably diminished due to factors such as unadjusted measures, risk stratification, and reliance on input distribution21.

Another factor contributing to the disparity between our findings and previous research could be the differences in the measurement and eGFR calculation methods. Moreover, there is a lack of standardized approach for measuring renal volume using CT scans, and the methods differ in terms of software, equipment, and procedures. These include variations such as ReRCoV, total parenchymal three-dimensional renal volume, renal cortical volume, kidney function cortical volumetry (RCoV), and the ellipsoid method19,22. According to a study, it was claimed that RCoV is the most effective volumetric method for predicting post-renal outcomes19. Furthermore, the absence of standardization in the quality of the arterial phase for corticomedullary differentiation of the kidney hinders the comparability of findings from other studies.

Regarding the calculation of eGFR, our study employed the CKD-EPI method, while another research used the four-variable Modification of Diet in Renal Disease (MDRD) equation. Additionally, a separate study compared the accuracy of three eGFR calculation methods but found them to be less reliable than the Chromium-51 labelled ethylenediaminetetraacetic acid radioisotope GFR23. Notably, in the context of evaluating kidney donors, CKD-EPI has demonstrated superior performance in eGFR measurement compared to MDRD, underscoring the absence of standardization in GFR measurement24. At our institution, the majority of surgical procedures were conducted using laparoscopic technique, with a preference for left kidney donation. This preference is primarily due to the left laparoscopic donor nephrectomy being less surgically intricate, owing to the anatomically longer renal vein25,26, facilitating vascular anastomoses. When dealing with kidneys featuring multiple renal arteries, we evaluate the length of vessels on a case-by-case basis. We opt for the side with less complex vasculature to mitigate the risk of post-transplant ischemia in the renal units. In cases of differing kidney functions, nuclear renal scintigraphy was assessed and the lower functioning kidney is chosen for transplantation. Donors with kidney stones are advised to have them removed before transplantation. Removal of small, uncomplicated renal stones in the chosen kidney can be done after nephrectomy promptly with endoscopy on the operating table to minimize ischemic time before proceeding with transplantation.

Our findings suggested that the residual renal volume is typically higher in left donor nephrectomies, implying that, in general, the right kidney is larger than the left, as supported by our data and previous studies27. This could potentially be a confounding factor influencing the results. Moreover, we identified male gender as a significant risk factor for chronic kidney disease (CKD). While numerous studies have reported similar findings, the underlying reasons for the connection between male gender and CKD in donor nephrectomy cases remain unclear20,28. Some studies have proposed that both age and male gender could impact the renal reserve capacity29,30. Additionally, a separate research study established a link between the cortex-aortic enhancement index and the decline in eGFR, particularly in relation to male donors28.

Our study has certain limitations. Primarily, it is a retrospective observational study, thus could have been influenced by incomplete data and potential biases. Additionally, there is a significant number of participants who were lost to follow-up, impacting the analysis due to the limited number of reported CKD cases. Finally, some participants who marginally met the criteria for CKD and subsequently showed improvement in the subsequent visit, only to experience a decline in eGFR, leading to them meeting the CKD criteria again. These cases essentially represent two distinct occurrences of CKD.