Tests and diagnosis

By Mayo Clinic Staff

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Diagnosing occupational asthma is similar to diagnosing other types of asthma. But with occupational asthma, your doctor will also try to identify whether a workplace irritant is causing your symptoms, and if so, what it may be. Your doctor will ask you a number of questions about your symptoms, your job and how they may be related. You'll need to provide a detailed description of working conditions at your present and previous jobs, and any possible asthma triggers you may have been exposed to.

An asthma diagnosis needs to be confirmed by tests that may include a lung (pulmonary) function test and an allergy skin prick test. Your doctor will want to make sure your symptoms aren't caused by another condition, such bronchitis. He or she may order blood tests, X-rays or other tests to rule out a cause other than occupational asthma.

Testing your lung function

Your doctor may ask you to perform lung function tests. These include:

  • Spirometry. This noninvasive test, which measures how well you breathe, is the preferred test for diagnosing asthma. During this 10- to 15-minute test, you take deep breaths and forcefully exhale into a hose connected to a machine called a spirometer. If certain key measurements are below normal for a person your age and sex, your airways may be blocked by inflammation (obstructed). This is a key sign of asthma. Your doctor may ask you to inhale a bronchodilator drug used in asthma treatment to open obstructed air passages. Then you retake the spirometry test. If your measurements improve significantly, it's likely that you have asthma.
  • Peak flow measurement. To determine if you have occupational asthma, your doctor may ask you to carry a peak flow meter, a small, hand-held device that measures how fast you can force air out of your lungs. The slower you are able to exhale, the worse your condition. You'll likely be asked to use your peak flow meter at selected intervals during working and nonworking hours. If your breathing improves significantly when you're away from work, you may have occupational asthma.
  • Nitric oxide test. This test is used to see how much nitric oxide gas is in your breath. High levels of nitric oxide can be a sign of asthma.

Tests for specific lung irritants

In an effort to identify what's causing your symptoms, your doctor may do tests to see whether you have a reaction to specific substances. These include:

  • Allergy skin tests. During a skin test, your skin is pricked with purified allergy extracts and observed for signs of an allergic reaction. These tests can't be used to diagnose chemical sensitivities, but may be useful to evaluate sensitivity to animal dander, mold, dust mites and latex.
  • Challenge test. During a challenge test, you inhale an aerosol containing a small amount of a suspected chemical to see if it triggers a reaction. Your lung function is tested before and after the aerosol is given to see whether it affects your ability to breathe.
May. 19, 2011