The criteria for suspecting occupational asthma include objective evidence of asthma, exposure to compounds known to cause OA, a latent period of exposure between the time of first exposure and the development of symptoms and a relationship between exposure and symptoms. All asthmatic patients should be questioned about occupation both past and present. This should include information on the processes involved in their workplace as well as other potential exposures in the working environment. Workers tend to be atopic and often notice symptoms of allergic rhinitis, conjunctivitis prior to developing chest symptoms. A clear relation ship may exist between the development of symptoms and exposure.
Immunological tests are often available to confirm sensitisation.
In, at least, some cases these chemicals bind to host proteins in the subjects airways altering its configuration and allowing the development of an immuno logical response. These patients can present with atypical histories with symptoms occurring late in the evening or at night when the patient is at home. Workers may not always be aware of the relationship between their symptoms and expos ure in the workplace. Risk factors Environmental factors which may be important for developing OA include the type and intensity of exposure to the sensitising agent. Clearly some agents such as isocyanates are more likely to induce symp toms than others.