The effect of body mass index on initiation of renal replacement therapy and mortality in stage 5 chronic kidney disease patients not receiving renal replacement therapy

Aim: This study aimed to evaluate the impact of body mass index (BMI) on mortality, renal replacement therapy (RRT) requirement, and renal function change in predialysis stage 5 chronic kidney disease (CKD) patients. Materials and Methods: A total of 524 predialysis stage 5 CKD patients were included in this retrospective cohort study. Patients were classified into six BMI groups: <18.5, 18.5–24.9, 25–29.9, 30–34.9, 35–39.9, and ≥40 kg/m². Demographic, anthropometric, and biochemical parameters were assessed. After one year of follow-up, mortality, RRT requirement, and glomerular filtration rate change (ΔGFR) were analyzed. Univariate and multivariate logistic regression analyses were performed to determine the independent effects of BMI and laboratory parameters (albumin, CRP, PTH, protein/creatinine ratio). Results: In the underweight group, mortality was 16.7% and RRT rate was 25%. In the normal BMI group, mortality was 5.5% and RRT requirement was the highest at 34.5%. Overweight and obese groups had lower rates. No significant difference was observed between groups for mortality (p=0.120), but RRT differed significantly (p=0.005). Low albumin was associated with increased risk of both mortality (p=0.038) and RRT (p<0.001). High CRP was an independent risk factor for mortality (p=0.018) and RRT (p=0.002). Increased protein/creatinine ratio was a strong predictor for both outcomes (p<0.001). PTH contributed only to RRT in univariate analysis (p=0.039). No significant association was found between BMI and ΔGFR (p=0.955). Conclusion: In predialysis stage 5 CKD patients, underweight and normal BMI groups represent the highest risk for mortality and RRT. Our findings suggest that the "obesity paradox" may also apply in this population and highlight the importance of evaluating BMI together with biochemical parameters in clinical Keywords: Chronic kidney disease, body mass index, obesity paradox, renal replacement therapy, mortality, proteinuria