Table 4

Odds ratios of developing ACPA-positive RA and ACPA-negative RA in subjects exposed to different combinations of smoking and SE alleles compared with never-smokers without SE alleles in MyEIRA

No SE

Any SE

Ca/Co

OR (95% CI)*

Ca/Co

OR (95% CI)*

ACPA-positive RA

Never-smokers

266/986

1.0

264/202

4.4 (3.5 to 5.6)

Ever-smokers

30/52

3.1 (1.7 to 5.7)

33/8

25.6 (10.4 to 63.4)

AP

0.7 (0.5 to 1.0)

ACPA-negative RA

Never-smokers

254/986

1.0

65/202

1.1 (0.7 to 1.7)

Ever-smokers

10/52

0.6 (0.2 to 2.0)

3/8

0.8 (0.1 to 4.8)

ACPA, anti-cyclic citrullinated proteins antibody; AP, attributable proportion due to interaction; Ca/Co, number of exposed cases/number of exposed controls; MyEIRA, Malaysian Epidemiological Investigation of Rheumatoid Arthritis; OR (95% CI), odds ratio and 95% confidence interval, adjusted for ethnicity, formal education, age, sex, residential area, *calculated by means of unconditional logistic regression to increase power; RA, rheumatoid arthritis; SE, shared epitope.

Too et al. Arthritis Research & Therapy 2012 14:R89   doi:10.1186/ar3813