Table 2.

Studies investigating the association of chronic obstructive pulmonary disease with risk of rheumatoid arthritis.

Reference	Study design	Population Sample (n) RA outcomes (n)	COPD exposure methods	RA outcome methods	Smoking and other adjustment variables	Effect size (95% confidence interval) for COPD and RA risk (reference group: no COPD)	Comments
De Roos AJ, Ann Epidemiol (2008) [81]	Case-control	Iowa & North Carolina, pesticide applicators and spouses (Agricultural Health Study) n=810 n=135 RA	Self-report (chronic bronchitis)	Physician-confirmed	No smoking adjustment Age, US state	Prevalent RA: OR 0.8 (0.3-2.2) Incident RA: OR 1.3 (0.3-5.7)	Cases were mostly prevalent RA; limited sample size and adjustment variables; also investigated other personal and family medical conditions
Bergström U, Rheumatology (2011) [97]	Nested case-control	Sweden (Malmö Preventive Medicine Program) n=1,450 n=290 incident RA	Presence and severity by GOLD criteria from research pulmonary function testing	Medical record review meeting 1987 ACR criteria	Smoking adjustment: not current/current Age, sex, socioeconomic status	Mild/stage I COPD: OR 1.34 (0.67-2.68) Moderate to very severe/stages II-IV COPD: OR 1.08 (0.59-1.99)	Pulmonary function tests were measured prospectively prior to RA diagnosis; suggestion of increased risk for RA among women with COPD, but not men; limited sample size and adjustment variables; also investigated restrictive lung disease
Sheen YH, J Allergy Clin Immunol Pract (2018) [75]	Case-control	Olmsted County, Minnesota (Rochester Epidemiology Project) n=439 n=221 RA	Not described	Billing and Berkson codes	No smoking adjustment No covariates	OR 0.62 (0.32-1.23)	Only unadjusted COPD results reported in this study that was focused on asthma; limited sample size

ACR, American College of Rheumatology; COPD, chronic obstructive pulmonary disease; GOLD, Global initiative for Obstructive Lung Disease; OR, odds ratio; RA, rheumatoid arthritis.