Impact of using different predictive equations on the prevalence of chronic byssinosis in textile workers in Pakistan

Byssinosis remains a significant problem among textile workers in low/middle-income countries. Here we share our experience of using different prediction equations for assessing 'chronic' byssinosis according to the standard WHO classification using measurements of forced expiratory volume in 1 s (FEV₁).

We enrolled 1910 workers in a randomised controlled trial of an intervention to improve the health of textile workers in Pakistan. We included in analyses the 1724 (90%) men who performed pre-bronchodilator spirometry tests of acceptable quality. We compared four different equations for deriving lung function percentage predicted values among those with symptoms-based byssinosis: the third US National Health and Nutrition Examination Survey (NHANES-III, with 'North Indian and Pakistani' conversion factor); the Global Lung Function Initiative (GLI, 'other or mixed ethnicities'); a recent equation derived from survey of a western Indian population; and one based on an older and smaller survey of Karachi residents.

58 men (3.4%) had symptoms-based byssinosis according to WHO criteria. Of these, the proportions with a reduced FEV₁ (<80% predicted) identified using NHANES and GLI; Indian and Pakistani reference equations were 40%, 41%, 14% and 12%, respectively. Much of this variation was eliminated when we substituted FEV₁/forced vital capacity (FVC) ratio (

Accurate measures of occupational disease frequency and distribution require approaches that are both standardised and meaningful. We should reconsider the WHO definition of 'chronic' byssinosis based on changes in FEV₁, and instead use the FEV₁/FVC.