Table 1.
Demographic characteristics and spirometry results stratified by diagnostic criteria
| Participant characteristics | LLN+/FR+
|
LLN−/FR+
|
LLN−/FR−
|
||
|---|---|---|---|---|---|
| N (%)a | p-valueψ | N (%)a | p-value$ | N (%)a | |
| Subjects | 527 | 324 | 1,753 | ||
| Male | 292 (55.4) | 0.056 | 196 (60.5) | 0.145 | 889 (50.7) |
| Age (years) | |||||
| Mean (SD) | 61.5 (9.8) | 0.0001* | 68.6 (7.2) | 0.0001* | 58.6 (10.5) |
| 40–49 | 81 (15.4) | 3 (0.9) | 436 (24.9) | ||
| 50–59 | 139 (26.4) | 41 (12.7) | 523 (29.8) | ||
| 60–69 | 185 (35.1) | 130 (40.1) | 484 (27.6) | ||
| 70–79 | 122 (23.1) | 150 (46.3) | 310 (17.7) | ||
| Ethnicity | |||||
| White | 472 (89.7) | 300 (92.6) | 1,477 (84.4) | ||
| Afro-Caribbean | 10 (1.9) | 6 (1.9) | 76 (4.3) | ||
| Asian | 26 (4.9) | 7 (2.2) | 127 (7.3) | ||
| Mixed | 5 (1.0) | 0 (0.0) | 25 (1.4) | ||
| Other | 14 (2.7) | 11 (3.4) | 49 (2.8) | ||
| BMI (kg/m3) | |||||
| Mean (SD) | 29.1 (6.5) | 0.0001* | 29.9 (6.0) | 0.03 | 30.5 (6.4) |
| <18.5 | 6 (1.1) | 2 (0.6) | 5 (0.3) | ||
| 18.5–24.9 | 127 (24.2) | 63 (19.5) | 280 (16.1) | ||
| 25.0–29.9 | 193 (36.8) | 121 (37.5) | 649 (37.3) | ||
| ≥30 | 201 (38.4) | 138 (42.7) | 819 (47.0) | ||
| Lung function | |||||
| FEV1 L (SD) | 2.19 (0.68) | 2.43 (0.64) | 2.81 (0.74) | ||
| zFEV1 (SD) | −1.59 (0.99) | 0.0001* | −0.69 (0.89) | 0.0001* | −0.32 (0.98) |
| FVC L (SD) | 3.73 (1.03) | 3.60 (0.94) | 3.62 (0.95) | ||
| zFVC (SD) | 0.01 (1.11) | 0.0001* | 0.07 (1.04) | 0.58 | −0.26 (1.00) |
| FEV1/FVC (SD) | 0.59 (0.08) | 0.67 (0.02) | 0.78 (0.05) | ||
| zFEV1/FVC | −2.48 (0.68) | 0.0001* | −1.28 (0.26) | 0.0001* | −0.16 (0.72) |
| Pack years | |||||
| Mean (SD) | 25.2 (21.4) | 0.0001* | 25.3 (27.6) | 0.0001* | 16.9 (20.1) |
| Smoking status | |||||
| Never | 71 (13.5) | 53 (16.6) | 422 (24.4) | ||
| Former | 212 (40.5) | 207 (64.9) | 843 (48.6) | ||
| Current | 241 (46.0) | 59 (18.5) | 468 (27.0) | ||
Notes: z prefix denotes the z-score for the lung function index.
a
Unless otherwise specified. The results for LLN−/FR+ were compared with LLN+/FR+ ($) and results for LLN+/FR+ were compared with LLN−/FR− (ψ) using Pearson Chi-square test for sex differences and Kruskal–Wallis tests for the other indices.
*
p-values ≤0.001 are significant in accordance with Bonferroni correction for multiple comparisons.
Abbreviations: FEV1, forced expiratory volume in 1s; FR, fixed ratio; FVC, forced vital capacity; LLN, lower limit of normal; BMI, body mass index.