How is Asthma Diagnosed?

To diagnose asthma, the doctor will see if three criteria are met:

• Recurring episodes where airflow becomes blocked, resulting in at least one of the asthma signs
• The blocked airflow can be at least partially reversed through medication
• Other potential causes of your symptoms are ruled out

Medical history

The doctor will evaluate the patient’s medical history to identify what symptoms they have had, when their symptoms occur, and how long they last. The intake includes establishing if the patient has experienced asthma symptoms while at rest, during exercise or after exposure to a known trigger. The doctor will also want to know if they have a family history of asthma, allergy, sinusitis, or nasal polyps.

Physical exam

The doctor will conduct a physical exam that focuses on the upper respiratory tract, chest, and skin. The doctor will listen for wheezing with a stethoscope and may look for nasal secretions, eczema, and similar allergy-related symptoms.

Lung function tests

Although the individuals symptoms, medical history and physical examination may suggest that they have asthma, lung (pulmonary) function tests may be needed to confirm an asthma diagnosis and to determine the severity of the disease. Lung function tests may include one or more of the following tests.

Spirometry

One of the most common tests and reliable ways to determine reversible airway obstruction is present is with spirometry. Spirometry is a test that measures the amount of air entering and leaving the lungs. Spirometry is a painless study and is generally used to diagnose asthma in adults and children over age 4.. Spirometry is frequently used to evaluate lung function in people with obstructive or restrictive lung diseases such as asthma or cystic fibrosis. This simple test can be performed in the physician's office and through this test the doctor will determine several values:

1. Vital capacity (VC), which is the maximum volume of air that can be inhaled or exhaled.
2. Peak expiratory flow rate (PEFR), commonly called the peak flow rate, which is the maximum flow rate that can be generated during a forced exhalation.
3. Forced expiratory volume (FEV1), which is the maximum volume of air expired in one second.

Spirometry uses a measuring device called a spirometer that is connected by a flexible tube to a disposable cardboard mouthpiece. The patient exhales and inhales deeply, then seals his or her lips around the mouthpiece and blows as forcefully and for as long as possible until all the air is exhaled from the lungs.

Ideally, the patient should exhale for at least 6 seconds. The spirometer measures the amount of air exhaled and the length of time it took to exhale it. The amount of air exhaled in the first second, expressed as "FEV1," is measured and compared to the total amount exhaled. If the amount exhaled in 1 second is disproportionately low to the total exhaled, the patient has an obstruction. The doctor will take the reading several times. The patient’s FVC and FEV1 results will be compared to what is normally seen in people without any blockage in their airways. From this data the doctor will have a good idea of how much "obstruction" is in the patient’s airways. To test for reversibility, the patient then inhales a bronchodilator (i.e., a drug that widens the airways in the lungs) and the spirometry is repeated. If the values of the test performed after administration of the bronchodilator are significantly better than the prebronchodilator values, the obstruction is considered reversible.

Sometimes a patient with asthma does not demonstrate reversibility after the inhalation of a bronchodilator. In this case, the patient may be treated for a few weeks with antiinflammatory medications and then returns for another spirometry test. If the posttreatment spirometry results are better than the initial results, the obstruction is considered reversible.

NEXT PAGE