Correlation between body mass index and early recovery outcomes after kidney transplantation

Abstract

BACKGROUND: The proportion of obesity in the Chinese population has increased year by year, but its impact on early renal function recovery after kidney transplantation has not been systematically elucidated, and localized research is urgently needed to provide evidence-based basis. OBJECTIVE: To investigate the effect of different body mass indexes on early renal function recovery in renal transplant recipients after surgery, to analyze the association between body mass index and postoperative creatinine, urine volume and hospital stay, and to propose clinical recommendations for individualized management. METHODS: The clinical data of 495 renal transplant recipients in the Second Xiangya Hospital of Central South University from 2019 to 2020 were retrospectively analyzed. According to the Chinese obesity standard, they were divided into a lean group (body mass index < 18.5 kg/m2, n=78), a normal group (18.5 ≤ body mass index < 24 kg/m2, n=273), an overweight group (24 kg/m2 ≤ body mass index < 28 kg/m2, n=119), and an obese group (body mass index ≥ 28 kg/m2, n=25). The baseline characteristics, postoperative creatinine, urine volume, and hospital stay were compared among the groups. Multivariate regression analysis was used to analyze the independent effect of body mass index on postoperative recovery. RESULTS AND CONCLUSION: (1) The age of the obese group was significantly higher than that of other groups (P < 0.001), the proportion of living donors (0%) was the lowest (P=0.015), the creatinine level on postoperative day 1 and hospital stay were the highest (P < 0.001), and urine volume was the lowest (P < 0.001); (2) Multivariate regression showed that for each 1 kg/m2 increase in body mass index, creatinine on postoperative day 1 increased by 38 μmol/L (β=0.38, P < 0.001), and urine volume decreased by 32 mL (β=-0.41, P < 0.001); (3) It is suggested that elevated body mass index is an independent risk factor for slow early renal function recovery and prolonged hospital stay after kidney transplantation; based on the Chinese obesity standard (body mass index ≥ 28 kg/m2), it is recommended to strengthen perioperative monitoring, optimize immunosuppressive regimens, and formulate individualized fluid management strategies for obese recipients to improve prognosis. This study can provide evidence-based basis for localized body mass index stratified management.

1. Introduction

Kidney transplantation is the best treatment option for patients with end-stage renal disease, and the quality of early postoperative renal function recovery directly affects graft survival and long-term patient prognosis [1-2]. Among the multiple factors influencing transplant outcomes, the clinical significance of recipient body mass index has attracted increasing attention in recent years. The World Health Organization defines obesity as a body mass index ≥ 30 kg/m² [3], but metabolic abnormalities in Asian populations often occur at lower body mass index levels. In China, a body mass index ≥ 28 kg/m² is used as the diagnostic criterion for obesity [4-5]. This population specificity suggests the need for a localized assessment system.

Existing studies have shown that obesity may affect kidney transplant prognosis through multiple mechanisms: inflammatory factors released by adipose tissue exacerbate ischemia-reperfusion injury [6-8], increased intra-abdominal pressure leads to insufficient graft perfusion [9-10], and insulin resistance increases the risk of immunosuppressant toxicity [11-13]. However, quantitative studies on the impact of body mass index on early postoperative recovery indicators remain controversial: LIESE et al. [14] showed in a study of 384 recipients that body mass index ≥ 35 kg/m² was an independent risk factor for delayed graft function and graft survival; whereas ORLIC et al. [15] found no significant effect of body mass index on early renal function. Notably, these studies mostly focused on Western populations and had small sample sizes, lacking systematic analysis of the Chinese kidney transplant population.

Existing domestic literature mostly focuses on the association between body mass index and long-term complications, and systematic research on the immediate postoperative recovery phase (such as creatinine decline rate, urine output recovery, and hospital stay) also has significant limitations [16-17]. Delayed early renal function recovery has been proven to be an independent predictor of acute rejection and graft loss [18-19]. Furthermore, current clinical guidelines have not yet formed standardized protocols for perioperative management of obese patients [20-21], especially individualized intervention strategies based on Chinese body mass index stratification that urgently need improvement [22-23]. Based on this, this study retrospectively analyzed 495 kidney transplant cases, stratified by body mass index according to Chinese obesity standards, and focused on exploring the quantitative association between different body mass index levels and early postoperative renal function recovery indicators (serum creatinine, urine output) and healthcare resource consumption (hospital stay), aiming to provide evidence-based basis for perioperative fluid management, immunosuppressive regimen adjustment, and complication prevention in obese recipients. The results will help establish a risk prediction model based on body mass index stratification and promote the development of precise perioperative management strategies.