Baseline characteristics of the study sample
Variable | All subjects | RA-UIP | RA-NSIP |
Subjects n | 137 | 108 | 29 |
Age years | 64.7±10.6 | 66.0±9.1 | 60.1±14.3 |
Female n (%) | 68 (50) | 52 (48) | 16 (55) |
Smoking history | |||
Available n | 135 | 106 | 29 |
Ever smokers n (%) | 87 (64) | 73 (69) | 14 (48) |
Pack-years | 31.8±23.1 | 33.6±24.1 (n=67) | 20.0±11.5 (n=12) |
Never smokers n (%) | 48 (36) | 33 (31) | 15 (52) |
Family history of RA | |||
Available n | 123 | 94 | 29 |
Family history of RA n (%) | 29 (24) | 23 (24) | 6 (21) |
Duration of RA preceding ILD years | 12.9±12.2 | 11.9±11.3 | 16.6±14.4 |
RA medications | |||
Methotrexate ever n (%) | 89 (65) | 67 (63) | 22 (71) |
Biologic agent ever n (%) | 87 (64) | 64 (60) | 23 (74) |
FVC | |||
Available n | 135 | 107 | 28 |
% pred | 69.3±19.2 | 69.7±18.5 | 67.8±21.9 |
FEV1 | |||
Available n | 134 | 106 | 28 |
% pred | 72.7±20.1 | 73.5±19.5 | 69.4±22.1 |
DLCO | |||
Available n | 108 | 84 | 24 |
% pred | 48.9±17.8 | 49.1±16.9 | 48.3±20.7 |
CPI | |||
Available n | 106 | 83 | 23 |
% pred | 47.2±14.7 | 47.0±13.9 | 47.6±17.6 |
Anti-CCP antibodies | |||
Available n | 80 | 61 | 19 |
CCP >20 n (%) | 66 (83) | 50 (82) | 16 (84) |
CCP titre for CCP positive | 140.5±87.1 | 143.6±85.1 | 130.5±95.0 |
RF | |||
Available n | 93 | 74 | 19 |
RF > 20 n (%) | 78 (84) | 64 (86) | 14 (74) |
RF titre for RF positive | 907.1±1754.7 | 1054.0±1914.0 | 336.8±462.3 |
Died n (%) | 54 (39) | 47 (43.5) | 7 (24) |
Median (IQR) follow-up years | 4.8 (2.5–7.8) | 4.6 (2.4–7.7) | 6.9 (4.1–8.1) |
Data are presented as mean±sd, unless otherwise stated. RA: rheumatoid arthritis; UIP: usual interstitial pneumonia; NSIP: nonspecific interstitial pneumonia; ILD: interstitial lung disease; FVC: forced vital capacity; FEV1: forced expiratory volume in 1 s; DLCO: diffusing capacity of the lung for carbon monoxide; CPI: composite physiologic index; CCP: cyclic citrullinated peptide; RF: rheumatoid factor; IQR: interquartile range.