Statistical Analyses
Patient demographics and clinical characteristics were summarized by weight category using means and standard deviations for continuous variables and frequencies and percentages for categorical variables.
A mixed effects linear regression model was used to determine if there was a significant change from baseline BMI over time among the cohort. This model included a fixed effect for BMI and a random effect for the patient. Covariates included in the model were patient baseline age at time of transplant, antigen mismatch, sex, relapse, malignant, ethnicity, TBI, and transplant source. Further, the relationship between the change in BMI over time and age was explored by including an interaction term between age and time.
Fisher’s exact test was used to determine if there were significant differences in the proportion of patients with GVHD (chronic and acute) and viral infections between the pre-transplant weight categories. The Kaplan-Meier method was used to estimate the median time to neutrophil and platelet engraftment and the overall survival rates at 5 years based on pre-transplant weight category.
Cox proportional hazards models were utilized to estimate the hazard ratio (HR) for overall survival, in addition to times to platelet engraftment and neutrophil engraftment, for patients in the overweight and obese pre-transplant weight categories versus patients in the normal weight/underweight pre-transplant weight category. Models were adjusted for age, transplant source, and mismatch. For overall survival, if patients did not die, they were censored at the time the data was pulled (i.e. December 31, 2019). For the analyses of time to neutrophil engraftment and time to platelet engraftment, a cause-specific hazards regression model was used to account for the competing risk of death for subjects who died before they could engraft. Patients were excluded if they were missing engraftment data due to death or transfer of care prior to engraftment. All HRs were accompanied by their corresponding 95% confidence interval (CI). SAS Version 9.4 (Cary, NC USA) was used for all statistical analyses. A p-value < 0.05 was considered statistically significant.