Occupational asthma screening using spirometry

Given that we know spirometry will detect few cases of OA not detected by questionnaire, but that it is still required/recommended by HSE as part of surveillance, do you have any consensus as to what cut offs for FVC and FEV1 (and ratio) could be given to screening nurses to identify cases for medical evaluation/SPF in the absence of symptoms? I can readily suggest limits with varying sensitivity and specificity but wondered if there was an evidence base to favour any particular set of criteria. A limit of 80% FEV/FVC seems to lack specificity with the result that many are over-investigated at inconvenience and worry to them. Clearly symptoms are the most important.

Occupational Asthma, Specialist, 2/20/2006, 2/20/2006,

Occupational asthma with no symptoms definately occurs, we have seen somebody like this recently with confirmed occupational asthma. In the same way that ordinary asthma and large changes in lung function can occur without symptoms (poor perceivers). The action levels for single measurements of lung function are unknown, it might be wise to see those clinically whose values are below the 95% confidence limits from the predicted equations. Of more relevance is the detection of those with a rapid decline in lung function. This is a complicated issue well investigated by eva hnizdo in OEM 2005;62:695. She has provided limits which relate to the site coefficient of variation and the the number of measurements. Changes over about 400ml are required between 2 measurements to be outside expected variation. The differences reduce with repeated measurements. If you have experience of setting action levels, please keep in touch as we are writing algorithms incorporating advice.

2/20/2006