Clinical characteristics of healthy controls, at-risk individuals who did not develop arthritis over time and at-risk individuals who developed arthritis. At-risk individuals have elevated titres for IgM-RF (>12.5 kU/L) and/or anti-CCP (>25 kAU/L). Healthy individuals have low titres for IgM-RF (≤12.5 kU/L) and anti-CCP (≤25 kAU/L)
| Healthy individuals (n=10) | At-risk individuals no arthritis developed (n=10) | At-risk individuals arthritis developed (n=11) | |
| Female sex, n (%) | 7 (70) | 5 (50) | 7 (64) |
| Age, years, median (IQR) | 34 (28–51) | 50 (39–60) | 48 (42–54) |
| IgM-RF positive, n (%) | 0 (0) | 7 (70) | 7 (64) |
| Level low positive, n (%)*† | – | 6 (86) | 4 (57) |
| Level high positive, n (%)*† | – | 1 (14) | 3 (43) |
| ACPA positive, n (%) | 0 (0) | 7 (70) | 9 (82) |
| Level, median (IQR)*‡ | – | 920 (549–2491) | 470 (144–1781) |
| IgM-RF/ACPA double positive, n (%) | – | 4 (40) | 5 (46) |
| ESR, median (IQR)§ | – | 3 (2–23) | 8 (7–15) |
| CRP, median (IQR)¶ | 0.9 (0.4–2.9) | 2.1 (1.6–6.3) | 6.2 (1.5–10.0) |
| 68TJC, median (IQR) | 0 (0) | 2 (0–7) | 4 (1–10) |
| 66SJC, median (IQR) | 0 (0) | 0 (0) | 0 (0) |
Positive IgM-RF: >12.5 kU/L.
Positive anti-CCP2 >25 kAU/L.
*Only in individuals who were positive.
†Levels were categorised into high/low positive according to cut-off levels used in the 2010 ACR/EULAR criteria for rheumatoid arthritis because of changed reference values over time.
‡Measured in kAU/L
§Measured in mm/hour.
¶Measured in mg/L.
ACPA, anticyclic citrullinated peptide antibodies (using anti-CCP2 test); CRP, C-reactive protein; ESR, erythrocyte sedimentation rate; IgM-RF, rheumatoid factor of the IgM isotype; 66SJC, swollen joint count assessed in 66 joints; 68TJC, tender joint count assessed in 68 joints.