Question 3. What is the approach to the patient suspected of having occupational asthma?

From Chapter 8 of the Philippine Consensus Report on Asthma 2004 by the Philippine College of Chest Physicians.
This guideline starts below.

What is the approach to the patient suspected of having occupational asthma?

Answer

As opposed to other occupational lung diseases like pneumoconiosis in which the diagnosis is based only on exposure history and chest x-ray abnormalities, occupational asthma needs to be confirmed by objective means.

The first step following history and physical examination is to confirm objectively that the patient has asthma. Spirometry before and after bronchodilator therapy should be assessed within 24 hours of typical workplace exposure or at a time when symptoms are present. If spirometry is normal, then bronchoprovocation using either methacholine or histamine should be performed to determine the presence or absence of airway hyperresponsiveness. A normal methacholine response in a symptomatic patient who is still working rules out occupational asthma.

Once the diagnosis of asthma is objectively confirmed by pulmonary function tests, the next step is to assess objectively the relationship of asthma to work. This could be done by challenge testing with the specific suspected agent or by serial monitoring of PEF for a period at work and a similar period away from work. Sensitivity and specificity of PEF monitoring in confirmed occupational asthma are 81% and 74%, respectively. Combining PEF monitoring with serial assessments of bronchial responsiveness using histamine or methacholine can provide further objective evidence. When the above results are inconclusive, serial spirometry performed throughout the work shift is advisable.

Early referral and rapid access to a specialist and a specialized center where investigations can be arranged is needed because the diagnosis is often difficult to establish in those who have left work and cannot or will not return.