What is the primary factor used to determine the severity of anorexia nervosa?

The primary factor used to determine the severity of anorexia nervosa is body mass index (BMI). BMI provides a standardized measure of body weight relative to height, allowing healthcare providers to assess an individual's nutritional status and severity of underweight conditions associated with anorexia nervosa. It is a critical component because lower BMI values typically correlate with more severe forms of the disorder, indicating greater health risks.

While other factors such as age, the duration of illness, and weight loss percentage play important roles in assessing the overall clinical picture and managing treatment, they do not have the same standardized approach for establishing severity as BMI does. For instance, two individuals may have similar weight loss percentages, but their BMI can indicate different health risks and levels of severity. Similarly, age might influence treatment approaches but does not directly determine the severity of the disorder itself as effectively as BMI does.