Diagnosing Work-Related Asthma: NIOSH Guidance for Clinicians

Guidance for health care providers from CDC's National Institute for Occupational Safety and Health (NIOSH).

Work-related asthma is diagnosed from a combination of the patient's medical and exposure history, a physical examination, and medical tests such as pulmonary function tests.

Think of it in every working patient

Consider work-related asthma in any patient who works — especially one with asthma that is new, or that has grown worse after being under control.

Ask screening questions about working conditions. If the answers point to a link, take a full work history, covering current and past job titles, what each job involved, and known exposures. Useful questions include:

• What kind of work do you do?
• Are you, or have you been, exposed to dust, fumes or chemicals at work?
• Are your breathing symptoms better or worse away from work, such as at weekends or on holiday?
• Do you think your health problems are related to your work?

The Agency for Toxic Substances and Disease Registry offers an occupational exposure history form.

What to look for

• Timing: symptoms may come on at work in response to an exposure, or hours later, after work.
• Severe cases: symptoms of severe work-related asthma may not ease away from work enough for a work pattern to show.
• Medication: rising use of a rescue inhaler can be an early sign that asthma is getting worse.
• Examination: findings are usually non-specific, and people with asthma often examine normally between attacks. Wheezing, if present, is usually heard on breathing out, though sometimes on breathing in as well.

A short time away from work

A brief period off work can help confirm the diagnosis. If pulmonary function improves while the patient is away — for example peak expiratory flow measured at home, or bronchial responsiveness measured by a methacholine challenge — that supports an occupational cause.

Conditions that can look like asthma

In adults, the differential diagnosis includes, among others:

• chronic obstructive pulmonary disease (COPD);
• non-asthmatic eosinophilic bronchitis;
• hypersensitivity pneumonitis;
• vocal cord dysfunction;
• obliterative bronchiolitis.

Tests

The American Thoracic Society publishes guidelines on performing and interpreting pulmonary function tests such as spirometry.

• Serial peak expiratory flow: teach the patient to use a peak flow meter and record readings four times a day on days off, before, during and after work on workdays, and before bed every day. Several weeks of records in a diary give the best picture; many meters store readings with date and time, which can be downloaded in the clinic.
• Bronchodilator reversibility: if spirometry shows airway obstruction, test whether an inhaled bronchodilator reverses it. Reversibility can support a diagnosis of asthma.
• Bronchial responsiveness: if spirometry is normal but asthma is still suspected, test for hyperresponsiveness with a methacholine or mannitol challenge.
• Exhaled nitric oxide: fractional exhaled nitric oxide marks allergic inflammation of the airways (the American Thoracic Society has guidelines on measuring it). A raised level supports allergic asthma but cannot tell work-related asthma from other asthma, and a normal level does not rule work-related asthma out.
• Allergy tests: blood tests for IgE antibodies to specific allergens, and skin prick, patch or intradermal tests for reactions to specific substances.

Some conditions make asthma worse, and further tests are needed to check for gastroesophageal reflux and rhinosinusitis.

Sources

• National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, "Diagnosing Work-related Asthma." https://www.cdc.gov/niosh/asthma/hcp/diagnosing/index.html
• The source page's photograph, a posed stock picture, is not reproduced. Its "gastroesophogeal" is corrected to gastroesophageal, and its garbled "four times a day on when off work" is read as four times a day on days off work.
• Rewritten in hubnx's own words.