BMI trends
The frequencies of BMI categories were compared at baseline, 100 days post-transplant, and at one-year time intervals until five years post-transplant. In the pre-transplant period, the percentage of individuals who were underweight (UW), normal weight (NW), overweight (OW), and obese (OB) were 5.4%, 54.5%, 22.2%, and 17.8% respectively (Table 2). At the five-year post-transplant mark, those numbers were 10.6%, 48.2%, 16.5%, and 24.7%, respectively.
The mixed effects linear regression model demonstrated a significant change from baseline BMI over time after controlling for age at transplantation, mismatch, sex, relapse, malignant, ethnicity, TBI, and transplant source, where BMI was found to increase 0.00094 ± 0.0001 kg/m2 each day after transplant (p < 0.001). In addition, TBI was significant, such that there was greater change in BMI from baseline in those who did not receive TBI compared with those who received TBI (1.288 ± 0.496, p = 0.010).
The inclusion of an interaction term between age and time further demonstrated distinct trends. Effects were estimated for the average 6-month-old, 2-year-old, 7-year-old, 12-year-old, and 16-year-old. While all patients overall experienced an increase in BMI over time that was more pronounced in older age groups (interaction effect between BMI and time: 0.000075 ± 0.00002, p < 0.001), a drop in BMI in the first 100 days post-transplant, though not significant, was observed in the 7-year, 12-year, and 16-year old (Figure 1). Patients 6 months and 2 years of age demonstrated an increase in BMI within the first 100 days post-transplant that was not statistically significant. After 100 days post-transplant, all age groups demonstrated significant increases in BMI measured per 100-day increment. These trends of increasing BMI relative to baseline, starting from day 100 to 5 years, were more drastic with each older age group.