Objective: A systematic epidemiological comparison of body weights of patients with anorexia nervosa can be enhanced by the use of age percentiles for the body mass index.
Method: To demonstrate the feasibility of this approach, body mass indices of 81 female adolescents with anorexia nervosa were calculated from anthropometric data upon admission for inpatient treatment and at follow-up and set into relationship to the age-dependent distribution of the body mass index in a large and representative sample of the German population. The percentiles were used to visualize the weight increase over time of each former patient by aligning the body mass index at referral with the respective body mass index at follow-up.
Results: Upon admission most adolescents had body mass indices below the third age centile. The distribution of body mass indices at outcome suggests a continuum between death of complications related to starvation, chronic anorexia, residual anorexia, and a low body weight Patients with very low body weights at referral had a poor prognosis, because their body weights tended to remain below the minimal normal weight for height. These conditions were statistically best described by categorical analysis, because they were nonlinear to a certain extent.
Discussion: The results indicate that the body mass index at referral influences the amount of weight that an individual patient gains in the future.