Body mass index in adolescent anorexia nervosa patients in relation to age, time point and site of admission

Body mass index (BMI) at admission is an important predictor of outcome in adolescent eating disorders. However, few studies have investigated BMI at admission, its changes in recent years, or modifying factors, such as duration of illness and age at onset in different geographical regions. Thus, this study aimed to investigate changes in BMI at admission over the past decade in one clinic, the differences in BMI between various treatment sites and the influence of duration of illness before admission and age at admission. Our sample consisted of 158 adolescent female patients with anorexia nervosa (AN) admitted between 2001 and 2009 to a major university hospital and 169 adolescent female patients recruited in a multicenter study between 2007 and 2010. We assessed the differences between departments in different regions of Germany in the multi-site sample. Changes over time in age-adjusted BMI and age at admission as well as modifying factors for age-adjusted BMI at admission, such as age at admission and duration of illness, were assessed in a representative local sample. There were no significant differences between departments in different regions of Germany. Over the course of the local study, there was a small but significant increase in the age-adjusted BMI score and absolute BMI at admission. In addition, there was a positive association between year of admission and age at admission. Older adolescents with AN had a lower age-adjusted BMI score and a longer duration of illness at the time of admission. The BMI at admission, which is one of the most important predictors of outcome in AN, has increased slightly during the past 10 years. Education strategies for parents and professionals should continue to be improved to further shorten the duration of illness before admission, especially for older adolescents.