Birmingham COPD Cohort: a cross-sectional analysis of the factors associated with the likelihood of being in paid employment among people with COPD

Figures & data

Figure 1 Participant flow chart for study participants from the Birmingham COPD Cohort Study.

Note: *Employment status data missing for one participant at the baseline visit.

Table 1 Sociodemographic, lifestyle, clinical, and occupational characteristics of COPD patients of working age recruited to the Birmingham COPD Cohort Study

Participant characteristics	Male, number (%); n=343	Female, number (%); n=265	Total number (%); n=608
Sociodemographic characteristics
Age categories (years)
38–49	40 (11.7)	28 (10.6)	68 (11.2)
50–59	125 (36.4)	128 (48.3)	253 (41.6)
60–64	178 (51.9)	109 (41.1)	287 (47.2)
Education level
Degree or higher level	33 (12.1)	25 (12.0)	58 (12.0)
A level/AS level or equivalent	21 (7.7)	15 (7.2)	36 (7.5)
GCSE, CSE, O level, or equivalent	73 (26.7)	67 (32.1)	140 (29.1)
No formal qualification	146 (53.5)	102 (48.8)	248 (51.5)
IMD score quintiles
$\begin{array}{l}1–2\hfill \\ 3\hfill \\ 4–5\hfill \end{array}\downarrow \text{increasing deprivation}$	110 (32.4)	74 (27.9)	184 (30.4)
	70 (20.6)	66 (24.9)	136 (22.5)
	160 (47.1)	125 (47.2)	285 (47.1)
Lifestyle characteristics
Smoking status
Never smoked	23 (7.2)	19 (7.9)	42 (7.5)
Ex-smoker	135 (42.5)	104 (43.2)	239 (42.8)
Current smoker	160 (50.3)	118 (49.0)	278 (49.7)
Clinical characteristics
MRC dyspnea grade
$\begin{array}{l}1\hfill \\ 2\hfill \\ 3\hfill \\ 4–5\hfill \end{array}\downarrow \text{Increasing breathlessness}$	81 (24.8)	44 (17.2)	125 (21.4)
	57 (17.4)	46 (18.0)	103 (17.8)
	68 (20.8)	62 (24.2)	130 (22.3)
	121 (37.0)	104 (40.6)	225 (38.6)
CAT score
$\begin{array}{l}\text{Low}(\text{high QOL})\hfill \\ \text{Medium}\hfill \\ \text{High}\hfill \\ \text{Very high}(\text{poor QOL})\hfill \end{array}\downarrow \text{Increasing symptom impact}$	40 (15.1)	26 (12.5)	66 (14.0)
	102 (38.5)	72 (34.6)	174 (36.8)
	87 (32.8)	79 (38.0)	166 (35.1)
	36 (13.6)	31 (14.9)	67 (14.2)
Degree of airflow obstruction (GOLD stage)a,b
Mild	91 (28.0)	84 (32.9)	175 (30.2)
Moderate	154 (47.4)	133 (52.2)	287 (49.5)
Severe to very severe	80 (24.6)	38 (14.9)	118 (20.3)
Exacerbations in the last 12 months
0	146 (47.7)	82 (33.7)	228 (41.5)
1–2	110 (36.0)	92 (37.9)	202 (36.8)
3+	50 (16.3)	69 (28.4)	119 (21.7)
Modified BODE index score quartilesa
$\begin{array}{l}1\hfill \\ 2\hfill \\ 3\hfill \\ 4\hfill \end{array}\downarrow \text{Increasing severity}$	103 (41.2)	82 (39.1)	185 (40.2)
	72 (28.8)	57 (27.1)	129 (28.0)
	46 (18.4)	49 (23.3)	95 (20.7)
	29 (11.6)	22 (10.5)	51 (11.1)
Number of comorbidities
0	64 (18.7)	25 (9.4)	89 (14.6)
1–2	140 (40.8)	110 (41.5)	250 (41.1)
3+	139 (40.5)	130 (49.1)	269 (44.2)
Comorbidities
Cardiovascular disease	155 (51.0)	113 (46.9)	268 (49.2)
Depression	86 (28.1)	95 (38.8)	181 (32.9)
Gastrointestinal disease	89 (27.2)	71 (28.4)	160 (27.7)
Osteoarthritis	42 (14.4)	47 (19.8)	89 (16.8)
Diabetes	46 (15.3)	27 (11.2)	73 (13.5)
Rheumatoid arthritis	29 (10.0)	37 (15.5)	66 (12.5)
Cancer	18 (6.0)	25 (10.3)	43 (7.9)
BMI categories
Underweight (<18.5)	8 (2.5)	8 (3.1)	16 (2.8)
Normal (18.5–24.9)	83 (25.5)	73 (28.4)	156 (26.8)
Overweight (25–29)	132 (40.6)	73 (28.4)	205 (35.2)
Obese (30–39.0)	96 (29.5)	76 (29.6)	172 (29.6)
Severe obesity (≥40.0)	6 (1.9)	27 (10.5)	33 (5.7)
Mean sit-to-stand repetitions (SD)	20.8 (6.6)	19.8 (6.6)	20.4 (6.6)
Occupational characteristics
Occupational background (SOC 2010)
Managers, directors, and senior officials	20 (5.9)	17 (6.6)	37 (6.2)
Professional	27 (8.0)	28 (10.9)	55 (9.2)
Associate professional and technical	28 (8.3)	11 (4.3)	39 (6.5)
Administrative and secretarial	5 (1.5)	48 (18.7)	53 (8.9)
Skilled trade	116 (34.2)	12 (4.7)	128 (21.5)
Caring, leisure, and other services	7 (2.1)	38 (14.8)	45 (7.6)
Sales and customer service	7 (2.1)	21 (8.2)	28 (4.7)
Process, plant, and machine operatives	87 (25.7)	39 (15.2)	126 (21.1)
Elementary	42 (12.4)	43 (16.7)	85 (14.3)
Exposures to VGDF in longest held job
$\begin{array}{l}\text{None}\hfill \\ \text{Low}\hfill \\ \text{Midium}\hfill \\ \text{High}\hfill \end{array}\downarrow \text{Increasing occupational airborne exposure}$	65 (19.2)	129 (50.4)	194 (32.6)
	129 (38.1)	73 (28.5)	202 (34.0)
	78 (23.0)	49 (19.1)	127 (21.3)
	67 (19.8)	5 (2.0)	72 (12.1)

Notes:

a Airflow obstruction based on postbronchodilator FEV₁ % predicted (mild: FEV₁ ≥80% predicted; moderate: 50% ≤ FEV₁ <80% predicted; severe: 30% ≤ FEV₁ <50% predicted, and very severe: FEV₁ <30% predicted);

b Includes 94 participants (male: n=38 and female: n=56) who did not have airflow obstruction on the day of assessment. Total numbers may differ due to some missing data.

Abbreviations: BMI, body mass index; BODE, body mass index, airflow obstruction, dyspnea, and exercise; CAT, COPD Assessment Test; COPD, chronic obstructive pulmonary disease; FEV₁, forced expiratory volume in 1 s; GOLD, Global Initiative for Chronic Obstructive Lung Disease; IMD, index of multiple deprivation; MRC, Medical Research Council; QOL, quality of life; SD, standard deviation; SOC, standard occupational classification; VGDF, vapors, gases, dusts, or fumes.

Table 2 Relationship between sociodemographic, lifestyle, clinical, and occupational characteristics and being in paid employment among working-age COPD patients

Characteristics	Number (%) employed n=248	Univariate model ORs (95% CI) for being employed	Final multivariable model ORs (95% CI) for being employeda
Sex
Male	147 (42.9)	1.0	1.0
Female	101 (38.3)	0.83 (0.60–1.15)	0.60 (0.36–1.01)
Age categories (years)
38–49	38 (55.9)	1.0	1.0
50–59	122 (48.4)	0.74 (0.43–1.27)	0.55 (0.24–1.26)
60–64	88 (30.7)	0.35 (0.20–0.60)	0.28 (0.12–0.65)
Education level
Degree or higher level	40 (69.0)	1.0	1.0
A level/AS level or equivalent	21 (58.3)	0.63 (0.27–1.50)	0.65 (0.23–1.90)
GCSE, CSE, O level, or equivalent	64 (45.7)	0.38 (0.20–0.72)	0.55 (0.25–1.25)
No formal qualification	68 (27.5)	0.17 (0.09–0.32)	0.43 (0.19–0.97)
Smoking status
Never smoked	19 (45.2)	1.0	1.0
Ex-smoker	103 (43.1)	0.92 (0.47–1.78)	0.98 (0.37–2.60)
Current smoker	106 (38.3)	0.75 (0.39–1.44)	0.79 (0.29–2.10)
Number of comorbidities
0	44 (50.0)	1.0	1.0
1–2	118 (47.2)	0.89 (0.55–1.45)	1.14 (0.52–2.49)
3+	86 (32.0)	0.47 (0.29–0.77)	0.70 (0.32–1.57)
MRC dyspnea grade
$\begin{array}{l}1\hfill \\ 2\hfill \\ 3\hfill \\ 4–5\hfill \end{array}\downarrow \text{Increasing breathlessness}$	79 (63.2)	1.0
	59 (57.3)	0.78 (0.46–1.33)
	67 (51.5)	0.62 (0.38–1.02)
	36 (16.0)	0.11 (0.07–0.18)
CAT score
$\begin{array}{l}\text{Low}(\text{high QOL})\hfill \\ \text{Medium}\hfill \\ \text{High}\hfill \\ \text{Very high}(\text{poor QOL})\hfill \end{array}\downarrow \text{Increasing symptom impact}$	42 (63.6)	1.0
	88 (50.6)	0.58 (0.33–1.05)
	52 (31.3)	0.26 (0.14–0.47)
	13 (19.7)	0.14 (0.06–0.31)
Degree of airflow obstruction
Mild	91 (52.0)	1.0
Moderate	111 (38.7)	0.58 (0.40–0.85)
Severe to very severe	38 (32.2)	0.44 (0.27–0.71)
Exacerbations in the last 12 months
0	106 (46.5)	1.0
1–2	91 (45.1)	0.94 (0.65–1.38)
3+	34 (28.6)	0.46 (0.29–0.74)
Modified BODE index score quartiles
$\begin{array}{l}1\hfill \\ 2\hfill \\ 3\hfill \\ 4\hfill \end{array}\downarrow \text{Increasing severity}$	116 (62.7)	1.0	1.0
	63 (48.8)	0.57 (0.36–0.90)	0.84 (0.48–1.47)
	25 (26.3)	0.21 (0.12–0.37)	0.38 (0.19–0.74)
	5 (9.8)	0.06 (0.02–0.17)	0.10 (0.03–0.33)
Exposures to VG
$\begin{array}{l}\text{None}\hfill \\ \text{Low}\hfill \\ \text{Midium}\hfill \\ \text{High}\hfill \end{array}\downarrow \text{Increasing occupational airborne exposure}$	94 (48.0)	1.0	1.0
	86 (42.6)	0.80 (0.54–1.19)	0.93 (0.51–1.71)
	47 (37.9)	0.66 (0.42–1.05)	0.91 (0.43–1.91)
	18 (24.7)	0.36 (0.19–0.65)	0.32 (0.12–0.85)

Notes:

a Multivariable model includes age, sex, smoking status, education level, number of comorbidities, modified BODE index, and exposures to VGDF;

b Airflow obstruction based on postbronchodilator FEV₁ % predicted (mild: FEV₁ ≥80% predicted; moderate: 50% ≤ FEV₁ <80% predicted; severe: 30% ≤ FEV₁ <50% predicted; and very severe: FEV₁ <30% predicted);

c Includes 94 participants (male: n=38; and female: n=56) who did not have airflow obstruction on the day of assessment. Total numbers may differ due to some missing data.

Abbreviations: BODE, body mass index, airflow obstruction, dyspnea, and exercise; CAT, COPD Assessment Test; CI, confidence interval; COPD, chronic obstructive pulmonary disease; FEV₁, forced expiratory volume in 1 s; GOLD, Global Initiative for Chronic Obstructive Lung Disease; MRC, Medical Research Council; OR, odds ratio; QOL, quality of life; VGDF, vapors, gases, dusts, or fumes.

Table 3 Relationship between the components of the modified BODE index and likelihood of being in paid employment

The BODE index components	Unadjusted OR (95% CI)	Adjusted ORa (95% CI)	P-value
B: BMI
>21	1.0 (reference)	1.0 (reference)
≤21	0.83 (0.46–1.50)	0.80 (0.33–1.92)	0.61
O: Airflow obstruction (postbronchodilator FEV1 % predicted)
≥65	1.0 (reference)	1.0 (reference)	P for trend =0.60
50–65	0.63 (0.40–0.98)	0.95 (0.47–1.89)
35–49	0.61 (0.37–1.01)	0.83 (0.39–1.77)
≤35	0.45 (0.21–0.95)	0.82 (0.25–2.71)
D: Dyspnea (mMRC score)
0–1	1.0 (reference)	1.0 (reference)	P for trend <0.01
2	0.69 (0.45–1.07)	1.18 (0.64–2.18)
3	0.14 (0.08–0.26)	0.23 (0.08–0.62)
4	0.11 (0.06–0.19)	0.36 (0.15–0.85)
E: Exercise capacity (modified to using sit-to-stand repetitions)
≥26	1.0 (reference)	1.0 (reference)	P for trend =0.09
21–25	0.71 (0.41–1.25)	0.84 (0.40–1.77)
16–20	0.36 (0.21–0.62)	0.80 (0.38–1.71)
≤15	0.13 (0.07–0.24)	0.41 (0.16–1.03)

Note:

a Adjusted for age, sex, smoking status, education level, number of comorbidities, exposures to VGDF, and the other components of the modified BODE index.

Abbreviations: BMI, body mass index; BODE, body mass index, airflow obstruction, dyspnea, and exercise; CI, confidence interval; COPD, chronic obstructive pulmonary disease; FEV₁, forced expiratory volume in 1 s; mMRC, modified Medical Research Council; OR, odds ratio; VGDF, vapors, gases, dusts, or fumes.