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Your doctor will ask about your child's symptoms, how long he or she has had them, how often they occur and whether you've noticed any factors that trigger the symptoms.

For example, your child's symptoms might start when he or she is running around or playing sports, or they might only come on at night.

Here's what your doctor is looking for:

• Coughing, with or without mucus
• Wheezing
• Shortness of breath
• A tight feeling in the chest
• Difficulty sleeping because of symptoms
• Symptoms that get worse at night
• Symptoms that get worse after exercise, with a cold, after contact with animals, when the weather changes, or when your child walks into a smoke-filled room
• Symptoms that come and go from day to day, week to week or month to month
• Changes in the shape of the chest caused by trying to overcome breathing problems.

Your doctor will also examine your child for physical signs of asthma and other allergic diseases, such as eczema, and might listen to his or her chest for any wheezing.

Noisy breathing has many different causes. For example, your child might have a another condition, such as a temporary infection caused by a virus. Your doctor has to be sure that your child doesn't have any of these conditions, so don't be surprised if you are asked a lot of questions about what your child has been doing.

Because conditions like asthma, eczema and hay fever tend to run in families, you'll probably also be asked about your own health and the health of your relatives.

Your doctor might be able to diagnose asthma just from what you tell him or her. But he or she might need to carry out some tests to help decide on the right diagnosis. Your child might be given a peak flow test or a spirometry test to measure how well their lungs are working.

Your child might also be asked to inhale an asthma medication. If this improves their symptoms, it may mean your child has asthma.

This is a simple test done by family doctors and asthma nurses. It can also be done at home. It is used to measure how easily your child can empty his or her lungs. Children with asthma can't breathe out as well as those without the condition, so this can help your doctor make a diagnosis.

A peak flow meter is shaped like a cylinder and has a scale down one side. It's about the size of a toilet-paper roll. To measure peak flow, your child will be asked to take a deep breath and breathe out as hard as he or she can into the mouthpiece of the meter. Your doctor might take a reading before and after your child uses a quick-relief inhaler (which contains a drug that helps to open up the airways). If your child's peak flow improves after taking the medication, it's usually a sign that he or she has asthma.

Your doctor might give you a prescription for a peak flow meter, which you can get from a drugstore. You can then measure your child's peak flow every day at home and keep a diary of readings. This helps you to monitor your child's asthma and check that the treatments he or she is taking are working.

This is another test to measure how your child's lungs are working, but it provides more detailed information than the peak flow test. A spirometerconsists of a mouthpiece attached by a tube to a computer with a readout.

Your child will be asked to breathe out as hard as he or she can into the mouthpiece. The spirometer will produce a graph. From the reading, your doctor will be able to tell whether your child's airways are narrowed or not. Children with asthma cannot breathe out as fast as normal, because of the narrowed airways.

If you're told your child has asthma, you might want to know how bad it is. Doctors grade asthma in children according to how often they get symptoms and what medications they need to keep the condition under control. To learn more, see How bad is my child's asthma?

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.