Diagnosis

Diagnosing asthma can be difficult. Signs and symptoms can range from mild to severe and are often similar to those of other conditions, including emphysema, early congestive heart failure or vocal cord problems. Children often develop temporary breathing conditions that have symptoms similar to asthma. For example, it can be hard to tell asthma from wheezy bronchitis, pneumonia or reactive airway disease.

In order to rule out other possible conditions, your doctor will do a physical exam and ask you questions about your signs and symptoms and about any other health problems. You may also be given lung (pulmonary) function tests to determine how much air moves in and out as you breathe.

Tests to measure lung function include:

• Spirometry. Measures the narrowing of your bronchial tubes by checking how much air you can exhale after a deep breath and how fast you can breathe out.
• Peak flow. A simple device that measures how hard you can breathe out. Lower than usual peak flow readings are a sign your lungs may not be working as well and that your asthma may be getting worse. Your doctor will give you instructions on how to track and deal with low peak flow readings.

Lung function tests often are done before and after taking a bronchodilator (brong-koh-DIE-lay-tur) such as albuterol to open your airways. If your lung function improves with use of a bronchodilator, it's likely you have asthma.

Other tests to diagnose asthma include:

• Methacholine challenge. If you have asthma, inhaling a known asthma trigger called methacholine will cause mild constriction of your airways. If you react to the trigger, you likely have asthma. This test may be used if your initial lung function test is normal.
• Nitric oxide test. This test is sometimes used to diagnose and monitor asthma. It measures the amount of a gas called nitric oxide you have in your breath. If your airways are inflamed — a sign of asthma — you may have higher than normal nitric oxide levels. This test isn't widely available.

How asthma is classified
To classify your asthma severity, your doctor will consider your answers to questions about symptoms (such as how often you have asthma attacks and how bad they are), along with the results of your physical exam and diagnostic tests. Determining the severity level of your asthma will help your doctor choose the best treatment for you. Asthma severity often changes over time, requiring an adjustment to treatment.

Asthma is classified into four general categories: 

Asthma classification	Signs and symptoms
Mild intermittent	Mild symptoms up to two days a week and up to two nights a month
Mild persistent	Symptoms more than twice a week, but no more than once in a single day
Moderate persistent	Symptoms once a day and more than one night a week
Severe persistent	Symptoms throughout the day on most days and frequently at night