Table 5.

Studies reporting smoking as a risk factor

	Study type	n	Comparison	Association with ILD	Adjusted for one or more baseline variables?	Grading
Juge et al15	Retrospective, multicentre cohort	1234	Ever smoker vs never smoker	p=0.53	Age, sex, country of origin	4
Li et al25	Retrospective, longitudinal, single-centre cohort	923	Ever smoker vs never smoker	OR 1.070 (95% CI 0.663 to 1.726); p=0.783	Age, sex, smoking, RA duration and severity, ACPA, RF	4
Paulin et al36	Prospective, single-centre cohort	118	Ever smoker vs never smoker	OR 5.85 (95% CI 2.12 to 16.09); p=0.001	Extra-articular manifestations, disease activity	3
Wang and Du27	Retrospective, single-centre cohort	544	Current smokers vs ex/never smokers	OR=1.71 (95% CI 0.67 to 4.38); p=0.263	Age, sex, steroid use, ACPA, RF, disease duration, HBsAg, Tripterygium wilfordii use	3
Doyle et al32	Prospective cohort, from two centres	189	Pack-years	p<0.1	No	3
Wickrematilake51	Retrospective, single-centre cohort	384	Ever smoker vs never smoker	p<0.0001	No	3
Salaffi et al30	Retrospective, single-centre cohort	151	Current smoker vs ex/never smoker	p=0.03	No	3
Furukawa et al33	Prospective, single-centre cohort	450	Ever smoker vs never smoker	p=0.2673	No	2
Yin et al37	Retrospective, single-centre cohort	285	Not stated	p=0.3	No	2

Grading was performed using Oxford criteria as detailed in the methods.

The remaining studies all reported unadjusted analyses with varying degrees of association (or no association) of smoking with ILD.27 30 32 33 37 51

ACPA, anticitrullinated protein antibodies; HBsAg, hepatitis B surface antigen; ILD, interstitial lung disease; RA, rheumatoid arthritis; RF, rheumatoid factor.