Three key circumstances may lead you to talk to your doctor about asthma:

If you think you have asthma.
Wheezing, difficulty breathing, pain or tightening in your chest, or coughing are common signs and symptoms of asthma. Wheezing, especially, is a frequent sign of asthma in children. However, some people with asthma never wheeze. Instead, they have recurrent, spasmodic coughs that are often worse at night. If you or your children have frequent coughs that last more than a few days or any other signs or symptoms of asthma, see your doctor.

If you know you have asthma.
If you know you have asthma, talk to your doctor about ways to manage your condition. Working as a team, you and your doctor can develop a plan to help you control your signs and symptoms, prevent an attack or stop an attack in progress. Don’t try to treat asthma yourself. Many asthma deaths result from a lack of proper treatment.

If your medication isn’t working.
Sometimes your medications may not offer the relief you need. Be sure to contact your doctor right away if a prescribed dosage of medication doesn’t work for you. In some cases you may not be using your inhalers correctly. Don’t try to solve the problem by taking more medication without consulting your doctor — overusing inhalers or taking too much medication can be dangerous.

Screening and diagnosis
Diagnosing asthma can be difficult.Signs and symptoms can range from mild to very severe and are often similar to those of other conditions, including emphysema, early congestive heart failure or vocal cord problems.
In order to rule out these and other possible conditions, your doctor will likely use several tests to arrive at a diagnosis. In most cases you’ll be asked to give a complete medical history and have a physical exam. You may also be given lung (pulmonary) function tests to determine how much air moves in and out as you breathe.

The two most common tools to measure lung function are:
Spirometer:A spirometer is used by a medical professional to measure narrowing of your bronchial tubes. This device measures the volume of air you can exhale after you’ve taken a deep breath.A spirometer also shows how quickly you can get air out of your lungs.

Peak-flow meter:A peak flow meter can be used at home to help detect subtle increases in airway obstruction before you notice symptoms.If the readings are lower than usual, it’s a sign your asthma may be about to flare up. Your doctor can give you instructions on how to deal with low readings.

Lung function tests often are done before and after taking a medication known as a bronchodilator to open your airways.If your lung function improves with use of a bronchodilator, it’s likely you have asthma.

If there is uncertainty about a diagnosis of asthma, your doctor may also recommend a methacholine bronchial challenge.If you have asthma, inhaling a known asthma trigger called methacholine will cause mild constriction of your airways, which can be measured with a lung function test. A positive methacholine test supports a diagnosis of asthma.