Characteristics of the study groups
| Healthy donors (N=32) | Individuals at-risk (N=63) | IgG ACPA-positive patient with RA (N=30) | IgG ACPA-negative patient with RA (N=29) | |
| Age, years: mean (SD) | 48 (12.7) | 48.3 (12.4) | 55 (11.6) | 59.8 (13.9)* |
| Female, N (%) | 20 (62.5) | 41 (65.1) | 18 (60.0) | 17 (58.6) |
| DAS28-ESR: mean (SD) | – | – | 2.46 (0.98) | 3.56 (1.66)†† |
| Disease duration, years: median (IQR) | – | – | 5 (1–10) | 2 (1–6) |
| Arthralgia, N (%) | – | 58 (92.1) | – | – |
| Arthralgia duration, months: median (IQR) | – | 23 (8.5–83) | – | – |
| IgA ACPA, µg/mL: median (IQR) | 2.1 (1.6–2.7) | 3.8 (2.4–7.7) | 4.47 (3.4–20.7) | 2.6 (1.0–4.5)‡ |
| IgA1 ACPA, µg/mL: median (IQR) | 1.8 (1.2–2.2) | 2.9 (1.8–6.3) | 3.5 (2.6–18.8) | 1.8 (0.8–3.1)‡ |
| IgA2 ACPA, µg/mL: median (IQR) | 0.4 (0.3–0.5) | 0.8 (0.4–1.7) | 1.0 (0.6–1.9) | 0.5 (0.3–0.9)‡ |
| IgG ACPA, RU/mL: median (IQR) | 0.9 (0.9–0.9) | 109.3 (14.1–334.6) | 78.1 (24.7–202.7) | 0.9 (0.7–1.0)‡ |
| IgA ACPA positive, %: low cut-off (high cut-off) | 15.6 (0) | 61.9 (41.3) | 86.7 (43.3) | 41.4 (17.2) |
| IgA1 ACPA positive, %: low cut-off (high cut-off) | 15.6 (0) | 60.3 (38.1) | 83.3 (46.7) | 37.9 (13.8) |
| IgA2 ACPA positive, %: low cut-off (high cut-off) | 15.6 (3.1) | 61.9 (34.9) | 76.7 (36.7) | 44.8 (3.4) |
| IgG ACPA positive, % | 0 | 80.9 | 100 | 0 |
Values of antibodies are represented as median (IQR).
*Older age in IgG ACPA-negative patients with RA compared with individuals at-risk (p=0.0007) and to healthy individuals (p=0.0022), ANOVA with Tukey’s multiple comparisons test.
†Higher DAS28 in IgG ACPA-negative patients with RA compared with IgG ACPA-positive (p=0.0034), unpaired t-test with Welch’s correction.
‡Higher ACPA levels in RA at-risk individuals and IgG ACPA positive RA patients compared with healthy individuals and IgG ACPA negative RA patients, Kruskal-Wallis test with Dunn’s multiple comparisons correction.
ACPA, anti-citrullinated protein antibodies; ANOVA, analysis of variance; DAS28, Disease Activity Score 28; ESR, erythrocyte sedimentation rate; RA, rheumatoid arthritis; RU, relative units.