Association of time-updated body mass index with initiation of kidney replacement therapy in patients with chronic kidney disease: results from the KoreaN Cohort Study for Outcomes in Patients With Chronic Kidney Disease (KNOW-CKD) study

Background: The association between body mass index (BMI) and risk of kidney replacement therapy (KRT) initiation in patients with non-dialysis-dependent chronic kidney disease (NDD-CKD) remains uncertain. Furthermore, controversies remain around baseline BMI as the only exposure in the analysis. Methods: A total of 2,136 patients enrolled in the KoreaN Cohort Study for Outcome in Patients With CKD were included in this study. The exposure was baseline and time-updated BMI. The outcome was initiation of KRT including dialysis or kidney transplantation during follow-up. A multivariable Cox proportional hazards model, a time-dependent Cox model without inverse probability weights, and a marginal structural Cox model were fitted, adjusting for both time-fixed and time-varying covariates including various clinicodemographic characteristics. Results: During the median follow-up of 8.3 years, KRT initiation occurred in 723 patients (34%). In patients with BMI ≥25.0 kg/m2, a higher time-updated BMI was significantly associated with a lower risk of KRT initiation compared to the reference group with normal BMI of 18.5-22.9 kg/m2, and a gradual decrease in risk of KRT initiation was observed with increasing BMI. The groups with BMI 25.0-29.9 kg/m2 (hazard ratio [HR], 0.73; 95% confidence interval [CI], 0.61-0.87) and BMI ≥30.0 kg/m2 (HR, 0.69; 95% CI, 0.53-0.88) exhibited a significantly lower risk of KRT initiation in the results of the marginal structural Cox model. Conclusion: A higher time-updated BMI has a lower risk of KRT initiation in obese patients with NDD-CKD. Therefore, aggressive reduction of body weight in patients with both obesity and CKD may not always be beneficial for adverse kidney events.