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7.9.2 AT-RISK POPULATIONS
Several hundred agents have been reported to cause occupational asthma and new causes are
reported regularly in the medical literature.
The most frequently reported causative agents include isocyanates, flour and grain dust,
colophony and fluxes, latex, animals, aldehydes and wood dust. 557-565
The workers most commonly reported to occupational asthma surveillance schemes include
paint sprayers, bakers and pastry makers, nurses, chemical workers, animal handlers, welders,
food processing workers and timber workers. 557,558,560,562-568
Workers reported to be at increased risk of developing asthma include bakers, food processors,
forestry workers, chemical workers, plastics and rubber workers, metal workers, welders, textile
workers, electrical and electronic production workers, storage workers, farm workers, waiters,
cleaners, painters, dental workers and laboratory technicians. 569-572
7.9.3 DIAGNOSIS
Occupational asthma should be considered in all workers with symptoms of airflow limitation.
The best screening question to ask is whether symptoms improve on days away from work.
This is more sensitive than asking whether symptoms are worse at work, as many symptoms
deteriorate in the hours after work or during sleep.
; Adults with airflow obstruction should be asked:
Are you better on days away from work?
Are you better on holiday?
Those with positive answers should be investigated for occupational asthma.
These questions are not specific for occupational asthma and also identify those with asthma
due to agents at home (who may improve on holidays), and those who do much less physical
exertion away from work. 573
Occupational asthma can be present when tests of lung function are normal, limiting their use
as a screening tool. Asthmatic symptoms improving away from work can produce false negative
diagnoses, so further validation is needed.
Serial measurement of peak respiratory flow is the most readily available initial investigation, and
the sensitivity and specificity of serial peak flow measurement in the diagnosis of occupational
asthma are high. 574-580
Although skin prick tests or blood tests for specific IgE are available, there are few standardized
allergens commercially available which limits their use. A positive test denotes sensitisation,
which can occur with or without disease. The diagnosis of occupational asthma can usually
be made without specific bronchial provocation testing, considered to be the gold standard
diagnostic test. The availability of centres with expertise and facilities for specific provocation
testing is very limited in the UK and the test itself is time consuming.
As a general observation, the history is more useful in excluding occupational asthma than in
confirming it. A significant proportion of workers with symptoms that improve on days away
from work or on holiday have been shown by objective tests not to have occupational asthma. 581
Expert histories have poor specificity compared with specific challenge testing. Free histories
taken by experts have high sensitivity but their specificity is lower. 582-587
d In suspected work-related asthma, the diagnosis of asthma should be confirmed using
standard objective criteria.
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