Diagnosing occupational asthma is similar to diagnosing other types of asthma. However, your doctor will also try to identify whether a workplace irritant is causing your symptoms and what it may be.
An asthma diagnosis needs to be confirmed by tests that may include lung (pulmonary) function tests and an allergy skin prick test. 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 — a key sign of asthma.
Your doctor has you inhale a bronchodilator drug used in asthma treatment, then retake the spirometry test. If your measurements improve significantly, it's likely you have asthma.
- Peak flow measurement. 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. A high level of nitric oxide can be a sign of asthma.
Tests for specific lung irritants
Your doctor may do tests to see whether you have a reaction to specific substances. These include:
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- Allergy skin tests. 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 in evaluating sensitivity to animal dander, mold, dust mites and latex.
- 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.
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