Choice of spirometric reference values for compensation assessment

Background and objective:   Two sets of local reference values are available for spirometry in Hong Kong, but it is uncertain how well they work in the assessment of occupational lung diseases. This study examined their relative performance in the compensational assessment of silicosis.
Methods:   Local reference values published in 1982 and 2006 were compared in two different populations comprising normal construction/quarry workers and silicosis patients. Only men aged 20–74 years were included.
Results:   The FVC results of 93 normal workers were significantly higher than those predicted by either the 1982 or the 2006 reference values. Compared with the 1982 reference values, the mean FEV₁% or FVC% was age-dependent and 5.2% higher in the normal workers. Smoking decreased the forced expiratory ratio, but did not show a major effect on FEV₁ or FVC among asymptomatic subjects. Despite their derivation largely from never-smokers, the 2006 reference values better predicted FEV₁ and FVC among all smoking categories. Among the 357 silicosis patients, the 1982 reference values also gave 8.8% higher FEV₁% and 7.4% higher FVC%. These spirometric values differed by more than 10% in patients aged 60 years or more. Despite the presence of disease, the mean FVC% was still significantly above 100%.
Conclusions:   Both the 1982 and 2006 local reference values underestimated the FVC of normal construction and quarry workers, reflecting possible occupational selection factors. The 2006 reference values outperformed the 1982 ones, especially among older subjects. Careful calibration with similar occupational groups in the same laboratory is highly desirable in the choice of spirometric reference values for compensation assessment. Smoking does not appear to affect this choice.