Occupational lung disease .8. The diagnosis of occupational asthma from serial measurements of lung function at and away from work

The diagnosis of occupational asthma has serious consequences for a worker, who is often left with much less money and no job (at least in the UK).(1) It is important that the diagnostic process is available and accurate. In most instances the diagnosis of occupational asthma can be strongly suspected from the history alone, by finding a temporal relationship between symptoms and occupational exposure. Some asthmatics substantially under or over report symptoms in relation to changes in lung function and not all workers can be relied on to tell the truth. It is therefore wise to obtain further proof of the diagnosis of occupational asthma before counselling workers to avoid exposures which might cost them their jobs. Managers usually require proof of a problem before money is allotted to remove or control occupational sensitising agents. For those still at work the most appropriate next step in the diagnostic process is the serial measurement of lung function in relation to work. Peak expiratory flow (PEF) has usually been selected as the most appropriate parameter to measure because of the availability of portable meters for its measurement. It is likely that similar changes will be shown in forced expiratory volume in one second (FEV(1)). Although some believe that the FEV(1) is more sensitive in detecting the airflow obstruction, particularly in the late asthmatic reaction,(2 3) not all agree.(3 4) If occupational asthma exists there should be measurable changes in PEF in relation to occupational exposure. The problem lies in differentiating the effects of work exposure from the spontaneous diurnal variation in airway calibre and its other determinants such as treatment, exercise, respiratory infection, exposure to non-specific irritants, and the errors inherent in its measurement.