Table 2.
Multivariable logistic regression analyses of the cross-sectional study sample
| No. Exposed | No. with ILD (%) | Adjusted OR* | 95% CI | P Value | ||
|---|---|---|---|---|---|---|
| RF/ACPA seropositivity | RF−/ACPA− | 341 | 6 (1.8) | Ref. | — | — |
| RF+/ACPA− or RF−/ACPA+ | 384 | 10 (2.6) | 1.48 | 0.52–4.24 | 0.46 | |
| RF+/ACPA+ | 1,603 | 84 (5.2) | 2.90 | 1.24–6.78 | 0.01 | |
| | ||||||
| RF titer analyses | ||||||
| RF titer category | Negative | 535 | 8 (1.5) | Ref. | — | — |
| Low positive (15–45 IU/ml) | 363 | 17 (4.7) | 2.69 | 1.11–6.51 | 0.03 | |
| High positive (>45 IU/ml) | 1,430 | 75 (5.2) | 3.40 | 1.61–7.18 | 0.001 | |
| RF titer quartiles | 1 | 583 | 9 (1.5) | Ref. | — | — |
| 2 | 582 | 22 (3.8) | 2.16 | 0.96–4.83 | 0.06 | |
| 3 | 581 | 21 (3.6) | 2.27 | 1.02–5.05 | 0.04 | |
| 4 | 582 | 48 (8.3) | 5.44 | 2.60–11.41 | <0.001 | |
| Log-transformed RF titer | Per 1 log-transformed unit | — | — | 1.40 | 1.22–1.59 | <0.001 |
| | ||||||
| ACPA titer analyses | ||||||
| ACPA titer category | Negative | 531 | 14 (2.6) | Ref. | — | — |
| Low positive (5–15 U/ml) | 94 | 1 (1.1) | 0.41 | 0.05–3.16 | 0.39 | |
| High positive (>15 U/ml) | 1,703 | 85 (5.0) | 1.91 | 1.04–3.49 | 0.04 | |
| ACPA titer quartiles | 1 | 582 | 15 (2.6) | Ref. | — | — |
| 2 | 582 | 18 (3.1) | 1.32 | 0.64–2.70 | 0.45 | |
| 3 | 582 | 29 (5.0) | 1.95 | 1.01–3.78 | 0.05 | |
| 4 | 582 | 38 (6.5) | 2.48 | 1.31–4.68 | 0.005 | |
| Log-transformed ACPA titer | Per 1 log-transformed unit | — | — | 1.17 | 1.05–1.30 | 0.004 |
Definition of abbreviations: ACPA = anti–citrullinated protein antibody; CI = confidence interval; DAS28 = Disease Activity Score in 28 Joints; ILD = interstitial lung disease; No. = number; OR = odds ratio; RA = rheumatoid arthritis; Ref. = reference; RF = rheumatoid factor.
*
Multivariable models are adjusted for age at enrollment, sex, race (white, African American, or other), smoking history, RA disease duration, and baseline articular disease severity (DAS28).