Table 1.
Characteristics of analyzed subjects in the Studies for the Etiology of RA at baseline (n=966).
| Characteristics | N (%), Mean (SD), or Median (IQR) |
|---|---|
| Age, years, mean (SD) | 47.2 (15.5) |
| Age ≥50 years, N (%) | 406 (42.0%) |
| Female, N (%) | 684 (70.8%) |
| Non-Hispanic white race, N (%) | 966 (100%) |
| Cumulative cigarette smoking pack-years, N (%) | |
| Never | 542 (56.3%) |
| >0 to ≤10 | 249 (25.9%) |
| >10 | 171 (17.8%) |
| Cigarette smoking status, N (%) | |
| Never | 542 (56.1%) |
| Past | 308 (31.9%) |
| Current | 116 (12.0%) |
| Body mass index, kg/m2, mean (SD) | 27.4 (6.1%) |
| Body mass index category, N (%) | |
| Underweight (BMI <18.5 kg/m2) | 12 (1.3%) |
| Normal (BMI 18.5 to <25 kg/m2) | 381 (39.9%) |
| Overweight (BMI 25 to <30 kg/m2) | 301 (31.5%) |
| Obese (BMI ≥30 kg/m2) | 261 (27.3%) |
| Education, N (%) | |
| ≤High school graduate | 187 (19.5%) |
| Some college or greater | 770 (80.5%) |
| Parity, N (%)* | |
| Parous | 161 (23.5%) |
| Nulliparous | 523 (76.5%) |
| Full GRS50, median (IQR) | 2.9 (2.5–3.6) |
| HLA GRS5, median (IQR) | 0.47 (0.0–1.2) |
| Non-HLA GRS45, median (IQR) | 2.5 (2.3–2.7) |
| Shared epitope alleles present, N (%) | |
| 0 | 436 (45.1%) |
| 1 | 443 (45.9%) |
| 2 | 87 (9.0%) |
| RA-related autoantibody positivity, N (%) | |
| RF by nephelometry | 48 (5.0%) |
| RF-IgA by ELISA | 33 (3.4%) |
| RF-IgM by ELISA | 52 (5.4%) |
| Any positive RF | 109 (11.3%) |
| Anti-CCP2 >5 units | 14 (1.5%) |
| Anti-CCP2 >2 units | 35 (3.6%) |
| Anti-CCP2 >5 units or RF by nephelometry | 59 (6.1%) |
| Anti-CCP2 >2 units or any positive RF | 137 (14.2%) |
| Inflammatory joint signs at RA-specific joints**, N (%) | |
| Any swollen joint | 80 (8.3%) |
| Any tender joint | 195 (20.2%) |
| Any swollen or tender joint | 222 (23.0%) |
| Any swollen MCP or wrist | 34 (3.5%) |
Parity was only considered for females.
RA-specific joints considered were metacarpophalangeal joints, proximal interphalangeal joints, wrists, elbows, and metatarsophalangeal joints. First metacarpophalangeal or metatarsophalangeal joints as well as swollen joints deemed to be due to trauma or degenerative disease were not included.
BMI, body mass index; anti-CCP2, anti-cyclic citrullinated peptide (2nd generation), ELISA, enzyme-linked immunosorbent assay, GRS, genetic risk score; HLA, human leukocyte antigen; IQR, interquartile range; MCP, metacarpophalangeal; RA, rheumatoid arthritis; RF, rheumatoid factor; SD, standard deviation.
Numbers of subjects with missing covariates: 4 for cumulative smoking, 11 for body mass index, and 9 for education. All subjects had complete data available on other covariates, including smoking status.