Introduction Asbestosis is commonly considered to be associated with slowly progressive pulmonary fibrosis. However, there is limited recent data to support this opinion. We set out to analyse the change in pulmonary function test (PFT) over time in a cohort of outpatients with asbestosis.

Methods Patients were identified retrospectively from a pool of clinic patients who had consented to participate in research. The diagnosis of asbestosis had been made on CT findings, history of asbestos exposure, exclusion of other causes of interstitial lung disease and agreement at occupational MDT. The PFT data from tests closest to the time of initial diagnosis were compared to the most recent PFT results. Parameters assessed were FEV₁, FVC, VC, TLC and KCO. The values were expressed as percentage predicted to ensure adjustment for age, weight etc. Annual change was calculated by dividing the total change by the number of years elapsed between PFT. Smoking status was also documented.

Results 57 patients were identified with a diagnosis of asbestosis. 9 had only had 1 set of PFT (awaiting follow-up) and hence were excluded leaving 48 patients. The mean time difference between PFT was 3.0 years (range 0.2–6.1 years). In 21 cases TLC had not been measured in one or both PFT and in 10 KCO had not been measured.

Conclusions As expected baseline FEV₁ decreased with increased smoking exposure. The other parameters at baseline were lower in those with the highest smoking exposure with the exception of TLC which was more varied. The greatest rate of change was seen in KCO% predicted, consistent with previous research. Unexpectedly the groups demonstrating the maximal decline in KCO were those with a low (<20 pack year) smoking history (7.2% annual decline) followed by lifelong non-smokers (3.9% annual decline). Those with the heaviest smoking history showed a lower rate of decline in all parameters compared to both non-smokers and the population as a whole. KCO and TLC were not performed in those with the most severe disease due to breathlessness, thus these results are likely to be an under-estimate of lung function changes.