Association between Body Mass Index and Early Renal Function after Kidney Transplantation: Observational and Mendelian Randomization Study.

Introduction: The relationship between BMI and early renal function recovery after kidney transplantation is important due to the rising global obesity rates.

Methods: A retrospective study on 320 patients who received allograft kidney transplantation at Guangxi Medical University Hospital explored the BMI-kidney function relationship using various statistical methods. Mendelian randomization (MR) was also employed to investigate causality.

Results: Based on the univariate analysis, multivariate linear regression models, and trend analysis, it was found that there were significant positive correlations between BMI and creatinine, urea, and cystatin C on the 7th day after kidney transplantation (p < 0.05). The sensitivity analysis further confirmed these correlations in different gender stratification, adolescents, and adults. However, the positive correlation with cystatin C was only significant in males. Additionally, after conducting smooth curve fitting analysis and threshold saturation analysis, it was revealed that the negative correlation between early renal function recovery was most significant when BMI was between 22.0 and 25.5 kg/m2, and early postoperative renal function may be optimal when BMI was at 22.2 kg/m2. Finally, the MR analysis confirmed a causal relationship between BMI and renal failure, as indicated by the IVW method (p = 0.003), as well as the weighted median estimator (p = 0.004).

Conclusion: This study on kidney transplant patients found that maintaining a BMI within the range of 22.0-25.5 kg/m2, with an optimal BMI of 22.2 kg/m2, improves early renal function recovery. This correlation holds true for different age-groups and genders. Monitoring and controlling BMI in high-risk patients can enhance post-transplantation renal function.