BMI and Anorexia

There are other factors to consider when looking at a diagnosis of anorexia.  Anorexia nervosa is defined by the American Psychiatric Association as a medical condition whereby individuals do not maintain a normal body weight, fear gaining weight, experience body image disturbances, and, in females, miss three consecutive menstrual cycles. Anorexia is an often fatal condition, and many individuals who have anorexia often have other psychological and physiological problems.  It is difficult to diagnose only knowing your daughter's BMI.  For a 15 year old female, however, a BMI of 13 seems incredibly low.  I would recommend you take her to see a pediatrician to confirm the diagnosis.  Good luck to both of you.