Diagnosing Work-related Asthma

Doctor taking notes

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Diagnosing work-related asthma is based on a combination of medical and exposure history, physical examination, and medical tests such as pulmonary function tests.

Consider work-related asthma as a possibility in all working patients. This includes those with new onset asthma or asthma that clinically worsens after previously being controlled. Ask patients screening questions about their working conditions. If their answers suggest a connection, obtain a comprehensive work history. The work history should include:

  • Current and past job titles
  • Job descriptions
  • Known exposures

Examples of work history questions include:

  • What kind of work do you do?
  • Are you now or have you previously been exposed to dust, fumes, or chemicals at your workplace?
  • Are your respiratory symptoms better or worse when away from work, such as on weekends or vacation?
  • Do you think your health problems are related to your work?
  • An electronic occupational exposure history form is available at the Agency for Toxic Substances and Disease Registry (ATSDR) website.

Evaluate the temporal relationship between clinical symptoms and the patient’s work schedule.

  • Symptoms of work-related asthma can occur at work in response to an exposure or might be delayed(occurring several hours after work such as in the evening).
  • Symptoms of severe work-related asthma might not improve away from work for a work-related pattern to be evident.

Document changes in asthma medication use.

  • An increase in using rescue inhalers can be an early indication that asthma is progressing.

Physical Examination

  • Exam findings are typically non-specific.
  • Patients with asthma often have normal physical examinations between asthma attacks.
  • If wheezing is present, it is generally on expiration. However, sometimes wheezing might also be auscultated on inspiration.

Temporary Work Furlough

A short period away from work period can help diagnose patients you suspect have work-related asthma. When away, improvements in pulmonary function tests such as ambulatory peak expiratory flow or bronchial responsiveness measured by methacholine challenge support an occupational etiology.

Differential Diagnosis

Some health conditions have symptoms similar to asthma. In adults, the differential diagnosis of asthma includes, but is not limited to, the following:

  • Chronic obstructive pulmonary disease (COPD)
  • Non-asthmatic eosinophilic bronchitis
  • Hypersensitivity pneumonitis
  • Vocal cord dysfunction
  • Obliterative bronchiolitis

Medical Tests

Pulmonary Function Tests

The American Thoracic Society has guidelines on how to perform and interpret pulmonary function tests.

Man taking Spirometry test

Photo by NIOSH

Peak Expiratory Flow

Serial measurements of peak expiratory flow might be useful for evaluating work-related asthma. Provide instructions to the patient on how to use a peak flow meter (spirometer). Ask the patient to record their peak expiratory flow:

  • Four times a day on when off work
  • On workdays (before, during and after work)
  • Before going to bed every day

Record measurements in a journal or diary over several weeks for best interpretations. Many spirometers automatically record measurements with date and time information. This can be downloaded from a clinical office for review.


Spirometry requires training to perform and interpret results. Practitioners who have limited experience with spirometry should refer patients to an occupational asthma specialist. For more information on spirometry, go to NIOSH’s Spirometry page.

Bronchodilator Reversibility Testing for Spirometry

When spirometry results show a patient has airways obstruction, the next step is to assess reversibility with an inhaled bronchodilator. The presence of reversibility supports an asthma diagnosis.

Nonspecific Bronchial Responsiveness (Bronchoprovocation Testing)

If spirometry is normal but asthma is suspected, bronchial hyperresponsiveness can be assessed using nonspecific bronchial responsive testing (e.g., methacholine or mannitol challenge tests).

Exhaled Nitric Oxide

  • Fractional exhaled nitric oxide is a marker of allergic airways inflammation.
  • The American Thoracic Society has guidelines on how to measure and interpret exhaled nitric oxide levels.
  • Increased fractional exhaled nitric oxide levels support allergic asthma diagnosis but does not differentiate between work-related asthma and non-work related.
  • A normal fractional exhaled nitric oxide level does not rule out work-related asthma.

Other Tests

  • Serologic testing to measure IgE antibodies for specific allergens.
  • Skin prick, patch, or intradermal testing to look for allergic reactions to specific substances.

Some medical conditions can make asthma worse. Additionally, other tests are needed to evaluate for gastroesophogeal reflux and rhinosinusitis.