Baseline characteristics of the study participants
| Characteristics | Total (N=4963) | Event (N=242) | Non-event (N=4721) | P value |
| Age (years), mean±SD | 68.89±9.50 | 68.88±9.82 | 68.89±9.48 | 0.988 |
| Male, n (%) | 3903 (78.64) | 182 (75.21) | 3721 (78.82) | 0.181 |
| Education, n (%) | 0.053 | |||
| Primary school and below | 2331 (46.97) | 132 (54.55) | 2199 (46.58) | |
| Junior high school | 1620 (32.64) | 67 (27.69) | 1553 (32.9) | |
| Senior high school and above | 1012 (20.39) | 43 (17.77) | 969 (20.53) | |
| BMI (kg/m2), mean±SD | 22.24±3.82 | 21.81±3.98 | 22.26±3.81 | 0.073 |
| Smoking status, n (%) | 0.001 | |||
| Never smoking | 1594 (32.12) | 92 (38.02) | 1502 (31.82) | |
| Ex-smoker | 2152 (43.36) | 116 (47.93) | 2036 (43.13) | |
| Current smoker | 1217 (24.52) | 34 (14.05) | 1183 (25.06) | |
| Medical history | ||||
| Severe exacerbation in the past year | 2869 (57.81) | 157 (64.88) | 2712 (57.45) | 0.022 |
| Ever regular long-acting bronchodilator treatment (≥3 months) | 1204 (24.26) | 65 (26.86) | 1139 (24.13) | 0.333 |
| Ever regular inhaled corticosteroid treatment (≥3 months) | 1154 (23.25) | 64 (26.45) | 1090 (23.09) | 0.228 |
| Ever home oxygen therapy | 800 (16.12) | 52 (21.49) | 748 (15.84) | 0.020 |
| Ever pulmonary rehabilitation | 534 (10.76) | 35 (14.46) | 499 (10.57) | 0.057 |
| FEV1%pred, median (quartile) | 43.51 (32.19, 60.34) | 38.57 (28.15, 53.56) | 43.78 (32.31, 60.71) | <0.001 |
| mMRC at admission, n (%) | 0.084 | |||
| <2 | 769 (15.49) | 28 (11.57) | 741 (15.70) | |
| ≥2 | 4194 (84.51) | 214 (88.43) | 3980 (84.30) | |
| CAT score at admission, n (%) | 0.003 | |||
| <10 | 392 (7.90) | 7 (2.89) | 385 (8.16) | |
| ≥10 | 4571 (92.10) | 235 (97.11) | 4336 (91.84) | |
| Laboratory test | ||||
| pH, mean±SD | 7.40±0.14 | 7.40±0.06 | 7.40±0.15 | 0.582 |
| PaO2 (mm Hg), mean±SD | 77.93±26.95 | 75.66±24.65 | 78.06±27.06 | 0.210 |
| PaCO2 (mm Hg), mean±SD | 45.08±12.87 | 47.76±14.24 | 44.93±12.78 | 0.002 |
| Neutrophil, median (quartile) | 5.00 (3.61, 7.12) | 5.42 (4.11, 8.24) | 4.97 (3.58, 7.07) | 0.001 |
| Eosinophil, median (quartile) | 0.10 (0.03, 0.22) | 0.10 (0.02, 0.23) | 0.10 (0.03, 0.22) | 0.517 |
| Lymphocytes, median (quartile) | 1.28 (0.90, 1.77) | 1.19 (0.82, 1.68) | 1.29 (0.90, 1.77) | 0.086 |
| Comorbidity/complication, n (%) | ||||
| Asthma | 459 (9.25) | 20 (8.26) | 439 (9.30) | 0.588 |
| Respiratory failure | 1239 (24.96) | 84 (34.71) | 1155 (24.47) | <0.001 |
| Pneumonia | 1465 (29.52) | 102 (42.15) | 1363 (28.87) | <0.001 |
| Chronic cor pulmonale | 1057 (21.30) | 88 (36.36) | 969 (20.53) | <0.001 |
| Coronary heart disease | 889 (17.91) | 52 (21.49) | 837 (17.73) | 0.137 |
| Hypertension | 1652 (33.29) | 77 (31.82) | 1575 (33.36) | 0.619 |
| Chronic heart failure | 280 (5.64) | 25 (10.33) | 255 (5.40) | 0.001 |
| Arrhythmia | 341 (6.87) | 18 (7.44) | 323 (6.84) | 0.721 |
| Diabetes | 537 (10.82) | 27 (11.16) | 510 (10.80) | 0.863 |
| Treatment during hospitalisation, n (%) | ||||
| Systemic corticosteroids | 1568 (31.59) | 97 (40.08) | 1471 (31.16) | 0.004 |
| Inhaled bronchodilator | 3632 (73.18) | 185 (76.45) | 3447 (73.01) | 0.240 |
| Methylxanthines | 3468 (69.88) | 196 (80.99) | 3272 (69.31) | <0.001 |
| Antibiotics | 4429 (89.24) | 230 (95.04) | 4199 (88.94) | 0.003 |
| Oxygen therapy | 3861 (77.80) | 186 (76.86) | 3675 (77.84) | 0.225 |
| Length of hospitalisation (days), median (quartile) | 10 (8, 13) | 11 (8, 13) | 10 (8, 13) | 0.085 |
Event: re-exacerbation within 30 days of discharge; non-event: no re-exacerbation within 30 days of discharge.
Values with p<0.05 are indicated in bold.
BMI, body mass index; CAT, COPD Assessment Test; COPD, chronic obstructive pulmonary disease; FEV1%pred, percentage-predicted forced expiratory volume in 1 s; mMRC, modified British Medical Research Council; PaCO2, artery carbon dioxide pressure; PaO2, arterial oxygen pressure.