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Smoking duration alone provides stronger risk estimates of chronic obstructive pulmonary disease than pack-years

Surya P Bhatt, Young-il Kim, Kathy F Harrington, et al.
Thorax 2018;0:1–8.

The probability of a correct diagnosis of chronic obstructive pulmonary disease (COPD) relies on quantification of risk factors and symptom burden. Cigarette smoking is the strongest risk factor for COPD, and a dose-effect relationship exists between smoking and those who develop COPD, even though no precise estimate of a threshold effect is available. Smoking burden is measured in pack-years, but the relative contributions to structural lung disease of cigarettes smoked per day versus duration is unknown.

Surya Bhatt of the University of Alabama has led a team in the analysis of cross-sectional data from a large multicentre cohort of current and former smokers. Detailed assessment of smoking history was made, including the age at which patients started smoking, duration of smoking and the number of cigarettes per day. Smoking burden was also assessed using the conventional metric of pack-years. The primary outcome was airflow restriction (forced expiratory volume in 1 second/forced vital capacity (FEV1/FVC)) and secondary outcomes included FEV1, computerised tomography (CT) emphysema, CT gas trapping, functional capacity and respiratory morbidity.

Smoking duration provided stronger risk estimates of COPD than cigarettes smoked per day and the composite index of pack-years. Giving equal weightage to cigarettes smoked per day and duration might attenuate the measured risk of association between smoking and COPD, resulting in miscalculation and biased estimates of disease risk.

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