Table 1. Characteristics of RA cases and controls in the Nurses' Health Study.
| RA cases (n = 542) | Controls (n = 551) | |
| Age, mean (SD)a | 55.3 (±8.1) | 55.5 (±7.9) |
| Current or past smoker, n (%) | 330 (62%) | 309 (56%) |
| Pack-years among smokers, mean (SD) | 25.0 (±18.0) | 22.7 (±20.9) |
| RA features | ||
| Mean age at symptom onset, mean (SD) | 55.7 (±10.8) | - |
| Mean age at diagnosis, mean (SD) | 56.6 (±10.2) | - |
| Rheumatoid nodules, n (%) | 70 (13%) | - |
| Rheumatoid factor positive, n (%) | 303 (56%) | - |
| Anti-CCP2 positive, n (%) | 112 (34%) | - |
| Seropositive, n (%) | 317 (58%) | - |
| Radiographic changes, erosions, n (%) | 163 (30%) | - |
| Seropositive and erosions, n (%) | 105 (19%) |
a
Age at blood draw for blood samples (n = 328 cases, n = 334 controls),
2
Cyclic citrullinated protein antibodies assayed in subset of NHS cases (n = 327) with stored blood samples at collected at different points with respect to RA onset, up to 12 years prior to onset or after diagnosis.