Clinical features of anorexia nervosa include:

• Weight maintained at least 15% below that expected for the person. In adults this normally represents a body mass index (BMI) of less than 17.5 kg/m².
• In people younger than 18 years of age, BMI centile charts should be used. A BMI below the 2.4th centile indicates underweight. In younger people, the diagnosis may be made in those who fail to gain weight during the expected growth spurt of puberty — they can become underweight without actually losing weight.
• Self-avoidance of foods thought to be fattening to achieve weight loss. One or more of the following compensatory behaviours may also be present:
• Self-induced purging (by vomiting or excessive use of laxatives).
• Excessive exercise.
• Use of appetite suppressants.
• Use of diuretics.
• Psychological features, which may include:
• Distortion of body image, with a dread of fatness.
• Over-evaluation of self-worth in terms of weight and shape leading to pursuit of thinness.
• Weight loss viewed as a positive achievement. The person perceives others as mistaken in believing they should gain weight.
• Denial of the seriousness of the weight loss or its impact on physical health.
• Difficulty acknowledging there is a problem and ambivalence about change.
• A widespread endocrine disorder involving the hypothalamic–pituitary–gonadal axis.
• This manifests in women as amenorrhoea (to fulfil the DSM-IV American Classification System criteria this is present for three or more menstrual cycles). It is important to note that monthly bleeding in women taking oral contraceptives is not an indicator of true menstrual status.
• Men may present with loss of libido and potency.
• Before puberty, growth and physical development can be affected.
• Other symptoms, such as constipation, headache, fainting, dizziness, fatigue, and cold intolerance.
• Physical signs, such as cachexia, acrocyanosis (hands or feet are red or purple in colour), dry skin, hair loss, bradycardia, orthostatic hypotension, hypothermia, loss of muscle mass and subcutaneous fat, oedema, and lanugo hair (downy hair on the upper part of the body and face).

[WHO, 1992; DSM-IV, 1994; Pritts and Susman, 2003; National Collaborating Centre for Mental Health, 2004]