Characteristics of ACPA-positive RA cases and controls
| Variables | Cases, ACPA positive (n=736) | Controls (n=872) | OR (95 % CI)* | p Value |
|---|---|---|---|---|
| No SE alleles (%) | 111 (15.08) | 414 (47.5) | Reference | <0.0001 |
| SE alleles, heterozygote (%) | 383 (52.04) | 373 (42.8) | 4.0 (3.1 to 5.1) | <0.0001 |
| SE alleles, homozygote (%) | 242 (32.88) | 85 (9.75) | 11.5 (8.1 to 16.1) | <0.0001 |
| Never smokers (%) | 207 (28.12) | 347 (39.79) | Reference | <0.0001 |
| Ever smokers (%) | 529 (71.88) | 525 (60.21) | 1.8 (1.4 to 2.2) | <0.0001 |
| Ever smokers, pack years† | ||||
| Never smokers (%) | 207 (28.2) | 347 (39.8) | Reference | <0.0001 |
| 0–9 (%) | 159 (21.6) | 219 (25.14) | 1.2 (1.0 to 1.6) | 0.084‡ |
| 10–19 (%) | 144 (19.6) | 134 (15.43) | 2.0 (1.6 to 2.6) | <0.0001‡ |
| 20– (%) | 225 (30.6) | 171 (19.63) | 2.6 (2.0 to 3.3) | <0.0001‡ |
| p Value for trend regarding OR for pack years | <0.0001‡ | |||
| Years since quitting smoking | ||||
| Never smokers | 207 | 347 | Reference | <0.0001 |
| 0–9 | 143 | 177 | 2.4 (1.8 to 3.1) | <0.0001 |
| 10–19 | 71 | 127 | 1.7 (1.2 to 2.3) | 0.004 |
| 20 | 60 | 133 | 1.4 (1.0 to 2.0) | 0.08 |
| p Value for trend regarding OR for years since quitting | <0.0001 | |||
↵* OR and corresponding 95% CI adjusted for sex, age and residential area.
↵† Information regarding pack years missing for one case and one control.
↵‡ p Value for differences in proportions regarding pack years of smoking between cases and controls.
ACPA, anticitrullinated protein/peptide antibody; RA, rheumatoid arthritis; SE, shared epitope.