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. Early detection of occupational asthma is very important. If symptoms improve on weekends and vacation and are worse at work, the job is likely to be the source of the asthma, although this is not always the case. Asthma is common, and exacerbation at work may be coincidental.

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 these disorders in some adults with late onset asthma.
• Panic disorder can coincide with asthma or be confused with it.
• Gastroesophageal reflux disorder (GERD) is a common companion in asthma and may affect treatment.
• 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 tests known as 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:

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.

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 strongly suspected.
• 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 adults who actually have asthma.

Allergy Tests

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

Other Tests

Tests that either rule out other diseases or obtain more information about the causes of asthma include:

• A complete blood count.
• Chest and sinus x-rays.
• Computed tomography (CT) scans. CT scans may be helpful in certain cases, such as for determining wall thickness in airways in patients who are difficult to treat, which could signify a higher risk for lung damage.
• Examination of the patient's sputum for eosinophils (white blood cells that in high levels are associated with severe allergic asthma). One 2002 study suggested that treatment goals based on achieving a normal eosinophil count might effectively manage asthma.
• Researchers are investigating measurements of certain chemicals in sputum or exhaled air that indicate airway inflammation. Such chemical markers include nitric oxide and hydrogen peroxide. For example, high levels of nitric oxide in exhaled air is proving to be a simple and noninvasive way of diagnosing asthma.
• If aspirin-induced asthma (AIA) is suspected, a non-invasive test called acoustic rhinometry may be useful. A solution of lysine acetylsalicylic acid (L-ASA) is instilled into the patient's nostril. Patients who experience symptoms such as sneezing, itching, congestion, and secretion are likely to have AIA.