Table 1.
Baseline characteristics of the TIRx cohort
| All patients (n = 82) | Developing arthritis (n = 39) | No arthritis during follow‐up (n = 43) | P‐value c | |
|---|---|---|---|---|
| Demographics | ||||
| Women, n (%) | 66 (81) | 32 (82) | 34 (79) | 0·786 |
| Age, mean (range) | 51·8 (18–76) | 55·0 (25–76) | 48·9 (18–75) | 0·089 |
| Time to arthritis, median (IQR) | 6 (3 ‐ 24) | |||
| Follow‐up time, median (IQR) | 69 (57 ‐ 77) | |||
| Symptom duration | ||||
| 0–6 months n (%) | 15 (18) | 8 (21) | 7 (16) | 0·514 |
| 6–18 months n (%) | 37 (45) | 15 (38) | 22 (51) | |
| 18+ months n (%) | 30 (37) | 16 (41) | 14 (33) | |
| Risk factors | ||||
| Ever smoker, n (%) | 39 (48) | 19 (49) | 20 (47) | 1 |
| Never smoker, n (%) | 43 (52) | 20 (51) | 23 (53) | |
| Shared epitope carrier, n (%) | 52 (64) a | 24 (62) | 28 (67) b | 0·82 |
| Antibodies | ||||
| RF positive, n (%) | 24 (30) | 16 (41) | 8 (19) | 0·031 |
| IgA ACPA‐positive, n (%) | 19 (23) | 10 (26) | 9 (21) | 0·794 |
| IgM ACPA‐positive, n (%) | 12 (15) | 9 (23) | 3 (7) | 0·06 |
| SC ACPA‐positive, n (%) | 17 (21) | 12 (31) | 5 (12) | 0·055 |
| IgG ACPA level (U/ml, mean ± s.d.) | 229 ± 489 | 340 ± 586 | 128 ± 359 | 0·213 |
| IgA ACPA level (U/ml, mean ± s.d.) | 10 ± 17 | 24 ± 65 | 7 ± 9 | 0·584 |
| IgM ACPA level AU/ml, mean ± s.d.) | 6 ± 16 | 10 ± 23 | 3 ± 2 | 0·003 |
| SC ACPA level (AU/ml, mean ± s.d.) | 89 ± 118 | 130 ± 156 | 52 ± 45 | 0·082 |
| Isotype usage | ||||
| One, n (%) | 56 (68) | 26 (67) | 30 (70) | 0·014 |
| Two, n (%) | 12 (15) | 2 (5) | 10 (23) | |
| Three, n (%) | 6 (7) | 4 (10) | 2 (5) | |
| Four, n (%) | 8 (10) | 7 (18) | 1 (2) |
Demographics analysed using Fisher’s exact test, symptom duration using Pearson’s χ2 test, risk factors using Pearson’s χ2 or Fisher’s exact tests, antibodies using Fisher’s exact test or Mann–Whitney U‐test and isotype usage using Pearson’s χ2 test.
IQR= interquartile range, RF= rheumatoid factor, ACPA= anti‐citrullinated protein antibodies, SC= secretory component‐containing; s.d. = standard deviation; Ig = immunoglobulin; TIRx = Swedish acronym for ‘extra‐early rheumatology follow‐up’.
a
Data from 81 patients;
b
data from 42 patients;
c
compared between the groups developing arthritis and no arthritis during follow‐up.