OBJECTIVE: The Diagnostic and Statistical Manual of Mental Disorders 5 suggests the 5th age-adjusted body mass index (BMI) percentile as the numeric cut-off for anorexia nervosa (AN) in children and adolescents. We aimed to investigate the degree to which the 5th age-adjusted percentile as the numeric cut-off for AN in youths reflects the clinical population of patients accepted for treatment.

METHOD: From a specialized eating disorder clinic, 305 patients with AN below 18 years of age were grouped according to age-adjusted BMI percentiles [below the 5th (low), above the 10th (high), and between the 5th and the 10th (medium)]. The distribution of eating disorder diagnoses and severity measured by the Eating Disorder Examination was compared.

RESULTS: Full-syndrome anorexia nervosa (F.50.0) was found in 182 (59.5%) patients and atypical anorexia nervosa (F.50.1) in 123 patients (40.5%). The number of patients in the low, medium, and high BMI percentile groups was 189 (62.0%), 34 (11.1%), and 82 (26.9%), respectively. Patients in the low BMI group differed from patients in the medium BMI group by a lower frequency of vomiting. The high BMI group presented with more weight and shape concern than the lower BMI group. Age was not a confounder of these associations.

DISCUSSION: We question the applicability of the 5th BMI percentile as a substantiated cut-off for the weight criterion in anorexia nervosa in youths and argue that the cut-off should not be ascribed great clinical importance as this may hinder early detection of illness and initiation of treatment.