Letter to the Editor

Renal handling of uric acid after kidney donation: a concern

for further study

There are many published papers ensuring thatkidney donation is a safe procedure. The follow-upstudies have focused mainly on glomerular filtra-tion (GFR) and the incidence of proteinuria beforeand after nephrectomy (Nx). However, the kidneyhas other functions, such as the excretion of uricacid (Uac), that have been systematically ignoredby researchers when analyzing the functionality ofthe remaining kidney among donors. This avoid-ance is worrisome because other studies conductedin non-kidney donors revealed that changes in theUac can be responsible for renal parenchymallesions (1, 2). Studies evaluating changes in serumuric acid after kidney donation are scarce, and noreports that assess the renal excretion of thisorganic compound exist.

We evaluated 21 kidney donors with average57 months post-Nx (range: 4–134 months). Theserum Uac increased from a baseline value of4.2 � 1.1 mg% to 5.4 � 1.6 mg% post-Nx

(p < 0.0001), but five of the 21 donors (24%) pre-sented serum Uac values higher than 6.0 mg%after Nx. We also measured the urinary Uac/creati-nine ratio in the urine (Uac/cr) collected over 24 hin all donors post-donation, and the average valuewas 0.36 � 0.10 mg/mg. Consequently, we sepa-rated the donors with a urinary Uac/crratio > 0.36 and those with a value ≤0.36 mg/mgafter the donation and verified the clinical and lab-oratory findings of the individuals in each group(Table 1). Interestingly, the donors who wereobese (BMI > 30 kg/m2) presented the lowestexcretion of uric acid and plasma triglyceride levelshigher than those of the leaner donors. In thegroup with a urinary Uac/cr ratio < 0.36 mg/mg,we found 5 of 12 (42%) with a serum Uac levelhigher than 6.0 mg%.It is possible that the expected increase in the

elimination of Uac by the remaining kidney isunable to occur, and in certain situations, the

Table 1. Characteristics of kidney donors after transplantation according to the urinary uric acid-to-creatinine ratio

Total group (n = 21)

Uric acid-to-creatinine ratio

p value>0.36 (n = 9) ≤0.36 (n = 12)

Female/Male (n) 16/5 8/1 8/4 0.89

Age (yr) 44.4 � 7.7 45.2 � 8.0 43.8 � 7.8 0.69

Time after the Nx (months) 57.0 � 48.8 67.3 � 44.9 49.2 � 48.3 0.39

BMI (kg/m2) 25.9 � 4.2 26.9 � 2.9 30.0 � 5.0a 0.04

SBP (mmHg) 120.7 � 12.8 119.1 � 15.5 122.0 � 11.0 0.62

DBP (mmHg) 80.4 � 8.1 80.1 � 9.2 80.7 � 7.6 0.88

Weight gain after donating (kg) 6.6 � 6.7 6.1 � 8.6 6.9 � 5.3 0.35

Waist circumference F/M (cm) 90.4 � 9.2/

101.0 � 5.3

88.7 � 6.2/97 92.1 � 11.9/

102.0 � 5.5

0.52

Serum uric acid 5.4 � 1.6 4.6 � 0.6 6.1 � 1.8a 0.03

Urinary uric acid excretion at 24 h (mg %) 525 � 144.2 596 � 177.1 472 � 122.2a 0.04

FEur (%) 10.4 � 4.7 13.8 � 1.6 7.9 � 0.7a 0.02

eGFR (mL/mim/1.73 m2) 67.5 � 17.9 66.6 � 21.5 68.1 � 15.8 0.52

Triglycerides (mg %) 175.8 � 77.0 130.6 � 26.5 209.8 � 85.7a 0.02

Urinary protein excretion (mg/24 h) 110.9 � 50.4 90.9 � 40.7 126.0 � 53.3 0.11

SBP, systolic blood pressure; DBP, diastolic blood pressure; BMI, body mass index; eGFR, estimated glomerular filtration rate; FEur, fractional excretion of

uric acid.a>0.36 vs. ≤0.36.

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© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd

Clin Transplant 2014: 28: 275–276 DOI: 10.1111/ctr.12326 Clinical Transplantation

reduction in excreted urinary uric acid combinedwith excess weight can cause an increase in theserum levels of this compound. However, thedecreased urinary excretion of uric acid mightsignal the presence of metabolic syndrome inthese individuals. Another hypothesis that shouldbe considered is whether the remaining kidney isable to increase its excretion of uric acid in thepresence of obesity in the kidney donors. Theprocessing of this organic compound in post-nephrectomy donors must be analyzed in studiesthat include larger numbers of individuals, andassessments of serum and urinary uric acid mustbe carried out during the evaluation of potentialkidney donors.

Sebasti~ao R. Ferreira-Filho, Fredric Oliveira andGlaucia Silva

Federal University of Uberlandia,Uberlandia, Brazil

e-mail: sebahferreira@gmail.com

References

1. FICOCIELLO LH, ROSOLOWSKY ET, NIEWCZAS MA et al.High-normal serum uric acid increases risk of early progres-sive renal function loss in type 1 diabetes: results of a 6-yearfollow-up. Diabetes Care 2010: 33: 1337.

2. BELLOMO G, VENANZI S, VERDURA C, SARONIO P, ESPOSITO

A, TIMIO M. Association of uric acid with change in kidneyfunction in healthy normotensive individuals. Am J KidneyDis 2010: 56: 264.

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Letter to the Editor