The validity of the fifth and the 10th Body Mass Index percentile as weight cut-offs for anorexia nervosa in adolescence: No evidence from quantitative and network investigation of psychopathology

Objective: Although the fifth Body Mass Index (BMI) percentile is the Diagnostic and Statistic Manual of Mental Disorders -5 weight cut-off criterion to diagnose anorexia nervosa (AN) in children and adolescents, its validity has not been proved, and the 10th percentile value is often applied. We aimed to investigate the diagnostic validity of these weight cut-offs. Method: We compared general and eating-disorder (ED) specific psychopathology in 380 adolescents with AN or atypical AN. They were grouped first with respect to the fifth BMI percentile and then with respect to the 10th BMI percentile and differences between groups were analysed. Network analyses on psychopathological symptoms were also conducted. Results: Adolescents with BMI above the fifth and the 10th percentile reported more severe ED specific symptomatology compared to those with BMI below these cut-offs. No significant differences emerged between groups neither in general psychopathology nor in the network structure of psychopathology. Conclusions: The fifth BMI percentile does not discriminate psychopathology severity in adolescents with AN. From the psychopathology perspective, our findings suggest that adolescents with atypical AN deserve the same clinical and research attention as those with full AN. Future studies are needed to identify a more accurate definition of underweight in adolescents