Diagnosis:

When asthma is suspected, the patient should describe for the doctor any pattern related to the symptoms and possible precipitating factors, including:

• Whether symptoms are more frequent during the spring or fall (allergy seasons).
• Whether exercise, a respiratory infection, or exposure to cold air has ever triggered an attack.
• Any family history of asthma or allergic disorders, such as eczema, hives, or hay fever.
• Any occupational or long-term exposure to chemicals. If symptoms improve on weekends and vacation and are worse at work, the job is the likely source of the asthma, although not always.

Ruling out Other Diseases

A number of disorders may cause some or all of the symptoms of asthma:

• Asthma and chronic obstructive lung diseases (chronic bronchitis and emphysema) affect the lungs in similar ways and, in fact, may all be present in the same person. Unlike other chronic lung conditions, asthma usually first appears in patients younger than age 30 and with chest x-rays that are normal. Still, it may be difficult to distinguish among these disorders in some adults with late onset asthma.
• Panic disorder can coincide with asthma or be confused with it.
• Other diseases that must be considered during diagnosis are pneumonia, bronchitis, severe allergic reactions, pulmonary embolism, cancer, heart failure, tumors, psychosomatic illnesses, and certain rare disorders (such as tapeworm and trichomoniasis).

Pulmonary Function Tests

If symptoms and a patient's history suggest asthma, the doctor will usually perform pulmonary function tests to confirm the diagnosis and determine the severity of the disease.

Using a spirometer, an instrument that measures the air taken into and exhaled from the lungs, the doctor will determine several values:

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

Spirometry is a painless study of air volume and flow rate within the lungs. Spirometry is frequently used to evaluate lung function in people with obstructive or restrictive lung diseases such as asthma or cystic fibrosis.

If the airways are obstructed, these measurements will fall. Depending on the results, the doctor will take the following steps:

• If measurements fall, the doctor typically asks the patient to inhale a bronchodilator. This drug is used in asthma to open the air passages. The measurements are taken again. If the measurements are more normal, the drug likely has cleared the airways and a diagnosis of asthma is likely.
• If measurement results fail to show airway obstruction, but asthma is still suspected, the doctor may perform a challenge test. This involves administering a specific drug (histamine or methacholine) that usually increases airway resistance only when asthma is present. The challenge test may be quite useful in ruling out occupational asthma. It is not always accurate, particularly in patients whose only symptom is persistent coughing.
• Administering cold air is another method for inducing airway resistance. This test is very accurate for ruling out asthma, but it is not sensitive enough to accurately identify asthma in adults.

Allergy Tests

The patient may receive skin or blood allergy tests, particularly if a specific allergen is suspected and available for testing. Allergy skin tests may help diagnose allergic asthma, although they are not recommended for people with year-round asthma.