Diagnosis

For adults and children over 5 years old, lung (pulmonary) function tests are used to check how well the lungs are working. Poor lung function is a sign that your asthma isn't well controlled. In some cases, lung function tests are also used in asthma emergencies to help your doctor understand the severity of an asthma attack or how well treatment is working.

Lung function tests include:

• Peak flow. Your doctor may take a peak flow reading when you come in for a scheduled visit or for emergency treatment during an asthma attack. This test measures how quickly you can breathe out. You may also use a peak flow meter at home to monitor your lung function.

  The results of this test are known as peak expiratory flow (PEF). A peak flow test is done by blowing into a mouthpiece as hard and as fast as you can with a single breath (expiration).

• Spirometry. During spirometry, you take deep breaths and forcefully exhale into a hose connected to a machine called a spirometer. A common spirometry measurement is forced expiratory volume, which measures how much air you can breathe out in one second.

  The results of this test are known as forced expiratory volume (FEV). Spirometry can also measure how much air your lungs can hold and the rate at which you can inhale and exhale.

• Nitric oxide measurement. This exam measures the amount of nitric oxide gas you have in your breath when you exhale. High nitric oxide readings indicate inflammation of the bronchial tubes.
• Pulse oximetry. This test measures the amount of oxygen in your blood. It's measured through your fingernail and only takes seconds.