Sex differences in uric acid levels in kidney transplant recipients and their donors: a preliminary retrospective cross-sectional study

Background: Higher serum uric acid (UA) levels are associated with poorer renal prognosis. In kidney transplantation, both donors and recipients are diagnosed as having chronic kidney diseases (CKD) based on renal function; however, their UA levels slightly vary. Elucidating the differences in UA would help improve kidney prognosis, especially for recipients. Therefore, we investigated UA levels in kidney transplant recipients by comparing them to those in their donors. Methods: In this retrospective cross-sectional survey, background information and blood examination results were collected from the donors just before donation and after transplantation in the donors and recipients. Associations between UA and sex estimated glomerular filtration rate (eGFR), and body mass index (BMI) were evaluated. Data were assessed by the Wilcoxon rank-sum test for continuous variables and the chi-squared test for categorical variables; multiple linear regression analyses were performed to determine which factors were associated with renal function before and after transplantation. Results: Participant characteristics were as follows. The mean donor age (n = 45, 16 men and 29 women) was 55 ± 11 years, and the mean recipient age (n = 45, 25 men and 20 women) was 46 ± 16 years. Sex-related differences (UA levels in men were predominant) existed in the UA of donors before (P < 0.001) and after donation (P < 0.001). Conversely, there were no significant sex-related differences in the UA of recipients (P = 0.51); the mean standardized eGFRs were similar in donors and recipients after transplantation. Multivariate linear regression analysis showed donor UA only correlated with donor sex before donation (P = 0.008). After donation, donor UA was associated with donor sex (P = 0.006), eGFR (P < 0.001), and BMI (P = 0.02). Notably, the UA of recipients after transplantation was only associated with eGFR (P = 0.003). Conclusions: Sex has less impact on UA in recipients than in donors. UA has a greater impact on renal prognosis in women than men, even at the same UA level. Therefore, attention should be given to UA levels in female recipients. These findings can be useful for determining patient prognosis following kidney transplantation in both donors and recipients