The clinical impact of kidney stones in a solitary kidney can be profound, leading to acute or chronic kidney disease. With this in mind, when evaluating potential kidney donors, approximately 25% of US transplant centers exclude living donor candidates with kidney stones [Citation1,Citation2]. This practice may be unnecessarily eliminating viable donor candidates.
Prior studies have noted an overall low incidence of post-donation kidney stones, even in donors with history of stones, and no increased risk of hospital encounters, hypertension, proteinuria, or reduced kidney function due to kidney stones [Citation2,Citation3]. The limited published data assessing long-term stone risk after donation has also been reassuring [Citation4,Citation5]. However, these studies have not included patients at increased metabolic risk for kidney stone formation. While urine metabolic testing appears to be limited in its ability to predict future recurrent stone formation [Citation6], at least six different transplant guidelines have recommended urine metabolic profile testing for potential kidney donors with stone risk [Citation7]. We therefore sought to elucidate the risk of developing kidney stones after kidney donation or candidate refusal in individuals with increased stone risk. We hypothesized that the absolute risk is low and similar in both groups.
We retrospectively reviewed our potential transplant donor database between 05/01/2018 to 06/30/2022 and sought to enroll those at increased risk for future kidney stones who were either refused or approved for donation (Institutional Review Board approval number: IRB_00154158). We defined increased risk based on 24-h urine stone work-up, a personal history of kidney stones, and/or incidental stone(s) on imaging (). We performed 24-h urine metabolic testing (calcium, oxalate, uric acid, and citric acid concentrations as well as supersaturation [Citation8] for calcium oxalate, calcium hydrogen phosphate, and uric acid) at a clinical laboratory (ARUP Laboratories, Salt Lake City, UT). A donor candidate was determined to have an abnormal urine metabolic profile if at least one of the urine test results exceeded the reference range provided by the laboratory (Table S1). We sent questionnaires to all eligible patients who agreed to participate in documenting stone development after donation/refusal. Our primary outcome was the occurrence of a kidney stone event. Secondary outcomes included time to kidney stone event and number of kidney stone events.
Figure 1. Flow chart of selection of the patients.
Of 144 potential donors at increased risk for stone formation, 69 agreed to participate and were included ( and Table S2). Among these, 30 had undergone donor nephrectomy, and 39 had not (19 were declined by the transplant center because of stone risk; 14 were declined for other reasons; 6 were approved but did not donate for other reasons). Median (interquartile range) age at donation/refusal was 43 (37–53) years, 45% were male, and 97% were White (). During the initial workup for the donation and no-donation groups, respectively, history of prior kidney stones was noted in 17% and 41% (p = 0.037); incidental stone was noted via CT in 30% and 28% (p = 1.00); and abnormal 24-h urine metabolic testing was noted in 73% and 82% (p = 0.40). However, the donation group had significantly fewer of these stone risks than the no-donation group (one risk, 80% vs. 51%; two risks, 20% vs. 46%; three risks, 0% vs. 3%; Cochran–Armitage test for trend test = 0.012). In addition, no individual in either group reported a subsequent stone event at a median post-donation/refusal period of 19.6 months (interquartile range: 13.0–33.1 months).
Table 1. Cohort characteristics.
Regarding limitations, this is a small, single-center study with a predominantly White population, and follow-up time was relatively short. As we investigated the post-donation/refusal stone events via self-reported recall on questionnaires without imaging studies, we could not assess for the possibility of asymptomatic stone formation.
In conclusion, no donor candidate developed kidney stones despite their increased risk. While larger and longer follow-up studies are needed to confirm the low risk of subsequent kidney stones in higher-risk donor candidates, those with an acceptable amount of stone risk should be considered viable donor candidates.
Author contributions
A.S. and M.Z.M. conceived this study. A.S., J.Y., I.E.H. and K.F. performed the chart review. J.Y. and M.Z.M. performed the data analysis. A.S., J.Y., I.E.H. and M.Z.M. wrote the first draft of the article. Every author has reviewed, edited, and approved the final article.
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The results of this paper have not been published previously in whole or part. The authors acknowledge participation in the Transplant Peer Review Network and complied with the journal’s author guidelines and policies.
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References
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