When making a diagnosis, your GP will probably ask questions about your weight and eating habits. For example, they may ask:

• if you have lost a lot of weight recently or quite quickly
• how you feel about your weight, and if you are concerned about it
• if you think you are overweight even though other people think you are thin
• if you make yourself vomit regularly
• (in women and girls) whether your periods have stopped, and if so, for how long

It is important to answer these questions honestly. Your GP is not trying to judge you or 'catch you out'. They just need to accurately assess how serious your symptoms are.

Weight and BMI

Your GP may check your weight. If someone has anorexia nervosa, their weight is generally at least 15% below average for their age, sex and height.

Your GP may also calculate your body mass index (BMI). A normal BMI for adults is 20-25. People with anorexia generally have a BMI below 17.5.

For more information on BMI and health, see the BMI healthy weight calculator tool.

Blood tests and other tests

Your GP may not need to carry out any tests to diagnose anorexia nervosa, but they will probably check your pulse and blood pressure.

If you have anorexia, you have a higher risk of developing some heart conditions, such as irregular heartbeat (arrhythmia). Sometimes an ECG (electrocardiogram) may be needed to check how well your heart is working.

Your GP may do blood tests to check the level of:

• fluids in your blood
• chemicals or minerals, such as potassium in your blood (see Anorexia - complications for more information).

However, blood tests can sometimes give normal results in an anorexic person who is very thin and has a very low body weight.

Referral to a specialist

If your GP thinks you may have anorexia, they may refer you to a specialist in eating disorders for a more detailed assessment - see Anorexia - treatment for more information. Your GP sometimes carries out this assessment.

Constipation

Constipation is when you pass stools less often than usual, or when you are having difficulty going to the toilet because your stools are hard and small.

Pain

Pain is an unpleasant physical or emotional feeling that your body produces as a warning sign that it has been damaged.

Thyroid gland

The thyroid gland in the throat makes hormones to help control growth and metabolism (the process that turns the food we eat into energy).