Longitudinal changes in body mass index and the competing outcomes of death and transplant in patients undergoing hemodialysis: A latent class joint modelling approach.

Aim: To characterise hemodialysis patients by BMI trajectories over the course of treatment and their association with the rates of transplant and death without transplant. Background(s): The relationship between body mass index (BMI) and patient survival in end-stage kidney disease in not well understood and has been the subject of much debate over recent years. Method(s): This study used a latent class joint modelling approach to identify latent groups that underpinned associations between patterns of change in BMI during hemodialysis and two competing events: Transplant and death without transplant. We included all adult patients who initiated chronic hemodialysis treatment in Australia or New Zealand between 2005 and 2014. Result(s): There were 16,414 patients included in the analyses; 2427 (14%) received a transplant, 6142 (35%) died prior to transplant, and 9122 (52%) were administratively censored. Our final model characterised patients based on five broad patterns of weight change (BMI trajectories): A "late BMI decline" (about two years after commencing hemodialysis); a "rapid BMI decline" (immediately after commencing hemodialysis); a "stable and normal or overweight BMI"; a "stable and morbidly obese BMI"; or an "increasing BMI". Mortality rates were highest amongst classes with declining BMI, and the timing of weight loss coincided with the timing of increases in mortality. The two stable BMI classes had relatively similar mortality rates, regardless of starting BMI (normal/overweight, or morbidly obese). Conclusion(s): Our results suggest that obesity is not necessarily protective in hemodialysis, but that the BMI trajectory is important, independent of BMI at dialysis initiation. Future research should be aimed at understanding the causes of weight changes during dialysis, to determine whether there could be strategies to improve patient survival.