Diagnosis

Your doctor will ask about your medical history and perform a physical exam. A thorough medical history and physical exam can provide important clues about a chronic cough. Your doctor may also order tests to look for the cause of your chronic cough.

However, many doctors opt to start treatment for one of the common causes of chronic cough rather than ordering expensive tests. If the treatment doesn't work, however, you may undergo testing for less common causes.

Imaging tests

• X-rays. Although a routine chest X-ray won't reveal the most common reasons for a cough — postnasal drip, acid reflux or asthma — it may be used to check for lung cancer, pneumonia and other lung diseases. An X-ray of your sinuses may reveal evidence of a sinus infection.
• Computerized tomography (CT) scans. CT scans also may be used to check your lungs for conditions that may produce chronic cough or your sinus cavities for pockets of infection.

Lung function tests

These simple, noninvasive tests, such as spirometry, are used to diagnose asthma and COPD. They measure how much air your lungs can hold and how fast you can exhale.

Your doctor may request an asthma challenge test, which checks how well you can breathe before and after inhaling the drug methacholine (Provocholine).

Lab tests

If the mucus that you cough up is colored, your doctor may want to test a sample of it for bacteria.

Scope tests

If your doctor isn't able to find an explanation for your cough, special scope tests may be considered to look for possible causes. These tests may include:

• Bronchoscopy. Using a thin, flexible tube equipped with a light and camera (bronchoscope), your doctor can look at your lungs and air passages. A biopsy can also be taken from the inside lining of your airway (mucosa) to look for abnormalities.
• Rhinoscopy. Using a fiberoptic scope (rhinoscope), your doctor can view your nasal passageways, sinuses and upper airway.