Baseline characteristics of pre-RA cases and controls, stratified by RF status at diagnosis or later in the cases
| All | RF-positive cases | RF-negative cases | ||||
|---|---|---|---|---|---|---|
| Characteristic | Cases (N=104) | Controls (N=174) | Cases (N=61) | Controls (N=103) | Cases (N=22) | Controls (N=39) |
| Mean age at screening, years (SD, range) | 46.0 (6.9, 32.9–60.8) | 46.0 (7.4, 32.5–60.4) | 44.8 (6.7, 32.9–60.6) | 44.7 (7.1, 32.5–60.2) | 47.5 (6.9, 34.1–60.4) | 48.3 (6.7, 34.8–60.4) |
| Mean age at diagnosis, years (SD, range) | 59.3 (9.4, 40.2–81.5) | NA | 57.6 (8.8, 40.2–79.5) | NA | 63.8 (9.1, 49.0–79.7) | NA |
| RF positive at diagnosis or later, n/N (%) | 61/83 (73) | NA | 61 (100) | NA | 0 | NA |
| Median time (years) to diagnosis (IQR, range) | 12.7 (8.4–19.4, 1–28) | NA | 12.4 (7.3–19.8,1–25) | NA | 16.1 (11.7–20.9, 2–28) | NA |
| BMI, kg/m2, mean (SD) | 24.3 (2.5) | 25.0 (3.6) | 24.1 (2.5) | 24.8 (3.8) | 24.8 (2.5) | 25.7 (3.1) |
| Current smokers, n/N (%) | 58/104 (56) | 79/174 (45) | 36/61 (59.0) | 45/103 (43.7) | 8/22 (36.4) | 19/39 (48.7) |
| ESR (mm), median (IQR, range) | 4 (3–8, 1–50) | 5 (3–7, 1–61) | 4 (3–8, 1–50) | 5 (3–5, 1–61) | 6 (4–7, 2–25) | 5 (4–7, 2–27) |
| Socioeconomic index, n/N (%) | ||||||
| Blue-collar workers, n/N (%) | 53/104 (52) | 80/174 (46) | 32/61 (52.5) | 47/103 (46) | 12/22 (55) | 18/39 (46) |
| White-collar workers, n/N (%) | 37/104 (36) | 71/174 (41) | 22/61 (36.1) | 39/103 (38) | 8/22 (36) | 18/39 (46) |
| Full self-reported health, n/N (%) | 73/104 (70) | 128/174 (74) | 43/61 (70) | 80/103 (78) | 15/22 (68) | 29/39 (74) |
| Self-reported diabetes, n/N (%) | 3/84 (3.6) | 2/140 (1.4) | 3/47 (6.4) | 2/80 (2.5) | 0/0 (19) | 0/35 (0.0) |
| Self-reported cancer (current or previous), n/N (%) | 2/84 (2.4) | 0/140 (0.0) | 1/47 (2.1) | 0/80 (0.0) | 1/19 (5.3) | 0/35 (0.0) |
| Self-reported cardiovascular disease, n/N (%) | 2/84 (2.4) | 0/140 (0.0) | 1/47 (2.1) | 0/80 (0.0) | 0/19 (0) | 0/35 (0.0) |
BMI, body mass index; ESR, erythrocyte sedimentation rate; RA, rheumatoid arthritis; RF, rheumatoid factor.