Living donor kidney transplantation (LDKT) is the best renal replacement therapy (RRT) for patients with advanced chronic kidney disease (CKD). It provides an improved survival of both graft and patient, and a low rate of surgical complications as it is a programmed intervention.1,2 In Spain, LDKT accounted for 11.4% of all kidney transplants performed in 2016.3 The benefits provided by this type of transplant in terms of morbidity, mortality and quality of life for recipients,4 plus the advances in surgical techniques, preparation and subsequent follow-up of the donor, have made possible to be more flexible in the necessary criteria for renal donation.

Renal donation does not imply biological benefits for those who voluntarily submit to it.

The evolution of renal function, morbidity and mortality in kidney donors has been discussed for years but the literature is not conclusive. Some classic studies with intermediate and long-term follow-up have ruled out a higher risk of CKD or death in renal donors as compared with the general population,5,6 however more recent studies using a better matched healthy control group, find a small increase in the absolute risk of CKD in the very long term, cardiovascular disease and even death in the kidney donor.7,8 This risk could be restricted to donors related to patients with genetic causes of renal disease.7 For all these reasons it is essential to carry out a meticulous and responsible selection process, informing about the risks to each potential donor and preserving the principle of autonomy in each patients.9

One year after donation, the remaining kidney manages to contribute up to 70% of renal function prior to nephrectomy.10 Recent studies indicate that in the remnant kidney, vasodilation and increased renal plasma flow (RPF) occur immediately after nephrectomy. These changes, together with a still not well characterized process of glomerular hypertrophy, make the glomerular filtration of the remaining kidney to increase approximately 40%, without a concomitant increase in the glomerular capillary pressure.11,12 The compensatory capacity of the remaining kidney, and consequently the renal function that the donor reaches are essential to assess the degree of morbidity associated to donation. The objective of our study was to estimate the prognostic value of renal function prior to nephrectomy r to estimate the compensation of subsequent renal function and if there are baseline factors related to the donor that allow us to predict the degree of renal recovery from the remaining kidney. Know the differences in the compensatory response between different subgroups of donors will be useful to inform future donors.

This was a retrospective observational study of a cohort of renal donors who consecutively underwent nephrectomy for renal donation between January 2001 and December 2015 at the Hospital del Mar, Barcelona.

The demographic, medical and analytical characteristics were analyzed considering baseline renal function and one year post-nephrectomy of the 66 donors who completed this follow-up period.

In this study living kidney donors we have analyzed the effect of the renal function prior to nephrectomy as well as other baseline variables on the ability to compensate for subsequent loss of renal function after nephrectomy. The evaluation of the renal compensation rate revealed that donors with higher creatinine, and therefore a lower baseline eGFR, compensated more than those with a higher eGFR. Most published studies analyzed the ability of renal donors to achieve a certain value of eGFR, generally greater than 60ml/min, considering that this function demonstrates an adequate evolution after donation. The proportion of donors that does not reach this value varies according to the series between 10 and 91%.15,16 Studies that assess the baseline factors associated with the recovery of baseline renal function agree that a higher baseline GFR predicts better renal function one year after donation.12 Our results are similar: a higher baseline FG is a predictor of reaching >60ml/min of eGFR a year after donation (data not shown). However, the suitability of this criterion for the evaluation of renal function is not clear. The GFR below 60ml/min which is considered to establish CKD in the general population17 is not applicable to healthy renal donors who, although suffering from a decrease in their renal mass, preserve the function of the remaining kidney.18,19

Numerous studies have described the process by which the remaining kidney increases the GFR after nephrectomy of the contralateral kidney. In humans, immediately after nephrectomy the renal flow increases, so that despite the fact that half of the renal mass is removed, the GFR reaches 70% of the previous renal function.10,12 Recent morphometric studies indicate that the flow increases in parallel to the renocortical volume and the ultrafiltration coefficient, calculated using mathematical models, and conclude that the increase in post-nephrectomy GFR can be explained exclusively by the increase in flow without an increase in glomerular pressure.11

Consistent with previous studies, in our donors, the mean eGFR one year after donation fell to around 30% of the previous GFR.16 Taking into consideration that optimal recovery is to reach 70% of baseline renal function at one year after nephrectomy, our objective was to study the evolution of renal function according to this criterion. Our results show that although donors with a higher baseline GFR are more likely to achieve a eGFR >60C/ml/min after one year, a lower baseline eGFR is associated with greater degree compensation after the completion of one year after donation. The analysis of the absolute loss of eGFR, revealed that the donors who lost >40ml/min of the baseline eGFR started with higher eGFR. This is due to the fact that the donors that compensate the most had a lowest absolute decrease in eGFR. The underlying physiological mechanisms that may explain this finding are unknown. A possibility is that individuals with a lower baseline GFR present more efficient compensation mechanisms (greater vasodilation capacity, greater glomerular hypertrophy, etc.). A limited number of studies in the literature have evaluated the rate of kidney compensation,14,15 therefore more studies are required and with longer follow-up time to analyze whether the renal compensation rate predicts the long-term evolution of renal function.

Apart from baseline renal function, no other characteristics were identified at baseline that could predict an adequate renal compensation rate one year after donation. Although there are studies that assess the importance of some factors to reach a eGFR >60ml/min after nephrectomy,6,16,20 there are only few studies that evaluate prognostic factors of renal compensation rate.15 The results on the influence of the different factors studied are not homogeneous. Some studies have described that patients with a higher body mass index are more likely not to reach a eGFR >60ml/min after nephrectomy,6,12 however this concept is not uniform among the authors.21 Age decreases the number of nephrons and increases the degree of arteriosclerosis.15 Although previous studies indicate that donors older than 60 years have lower renal function before and after nephrectomy,6,22 no significant differences were found in the percent of decrease in renal function as compared to younger donors. Dols et al.23 described that after an initial decrease in the GFR, that was not different in patients older or younger that 60 years, there was no evidence of an accelerated loss of eGFR being no different than in the general population: 5–10ml/min per decade. Recently, another study confirmed that the renal compensation rate does not differ according to age.15 Most studies have not demonstrated an effect of gender per se on the evolution of renal function after nephrectomy.14,20,22 Similarly, several publications associate the African-American race with a worse long-term evolution of renal function,24 although no short-term differences have been demonstrated after nephrectomy. There are also no uniform results about the role of arterial hypertension.20,25

The main limitation of our study is being unicentric retrospective observational and with a limited number of donors. The low ethnic variability and low prevalence of obesity among our donors makes difficult to explore the impact of these factors. In addition the GFR was not measured after one year of nephrectomy because it was not established in our routine clinical protocol.

In our experience, donors with higher creatinine and lower baseline GFR show the highest rate of renal compensation after the same period of follow-up. Only renal function reached significance as a predictor of the compensation rate. Further studies and longer follow-up are necessary to evaluate the suitability of the renal compensation rate as a criterion to evaluate the evolution of renal function in renal donors.

This study has been carried out, in part, thanks to the financing of the FIS-FEDER projects PI13/00598, FIS-FEDER PI16/00617 and RETIC Redinren FEDER RD16/0009/0013 (RedinRen).

The authors declare no conflict of interest related to the content of this article