Diagnosis

Diagnosing occupational asthma is similar to diagnosing other types of asthma. However, your doctor will also try to identify whether a workplace substance is causing your symptoms and what it may be.

An asthma diagnosis needs to be confirmed with lung (pulmonary) function tests and an allergy skin prick test. Your doctor 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 of 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 small hand-held device that measures how fast you can force air out of your lungs (peak flow meter). 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.

Tests for causes of occupational asthma

Your doctor may do tests to see whether you have a reaction to specific substances. These include:

• Allergy skin tests. Doctors will prick your skin with purified allergy extracts and observe your skin for signs of an allergic reaction. These tests can't be used to diagnose sensitivities to chemicals 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. Doctors test your lung function before and after the aerosol is given to see whether it affects your ability to breathe.