Prevalence of undiagnosed airflow obstruction among people with a history of smoking in a primary care setting

Figures & data

Table 1 Sociodemographic and clinical characteristics of subjects with history of smoking in primary care setting

Characteristics	Total (n=731)	Airflow obstruction: FEV1/FVC <0.7
		Yes (n=107)	No (n=624)	P-value*
Sociodemographic
Age (years; mean ± SD)	62.2±11.7	68.2±9.7	61.2±11.8	<0.001
Sex, n (%)				0.226
Male	676 (92.5%)	102 (95.3%)	574 (92.0%)
Female	55 (7.5%)	5 (4.7%)	50 (8.0%)
Education, n (%)				0.188
Primary or below	338 (46.2%)	59 (55.1%)	279 (44.7%)
Middle school	197 (26.9%)	29 (27.1%)	168 (26.9%)
High school	153 (20.9%)	14 (13.1%)	139 (22.3%)
University or above	26 (3.6%)	3 (2.8%)	23 (3.7%)
Unknown	17 (2.3%)	2 (1.9%)	15 (2.4%)
Occupation, n (%)				0.017
Retired	369 (50.5%)	72 (67.3%)	297 (47.6%)
Unemployed	36 (4.9%)	5 (4.7%)	31 (5.0%)
Housewife	18 (2.5%)	1 (0.9%)	17 (2.7%)
Working	237 (32.4%)	24 (22.4%)	213 (34.1%)
Others or unknown	71 (9.7%)	5 (4.7%)	66 (10.6%)
Smoking status, n (%)				0.948
Current smoker	353 (48.3%)	52 (48.6%)	301 (48.2%)
Daily smoker	329 (45.0%)	49 (45.8%)	280 (44.9%)
Nondaily smoker	24 (3.3%)	3 (2.8%)	21 (3.4%)
Past smoker	378 (51.7%)	55 (51.4%)	323 (51.8%)
Years since first smoking (years; mean ± SD)	42.9±12.9	50.1±11.3	41.6±12.8	<0.001
Pack-years (mean ± SD)	34.2±25.1	38.7±26.5	33.4±24.8	0.046
Clinical
Body weight (kg; mean ± SD)	66.9±11.4	65.0±12.4	67.3±11.1	0.056
Body height (m; mean ± SD)	1.6±0.1	1.6±0.1	1.6±0.1	0.924
BMI (kg/m^2; mean ± SD)	25.0±3.6	24.2±3.3	25.2±3.6	0.011
BMI cutoff, n (%)				0.010
Underweight (<18.5 kg/m^2)	14 (1.9%)	2 (1.9%)	12 (1.9%)
Normal (≥18.50–<23 kg/m^2)	197 (26.9%)	43 (40.2%)	154 (24.7%)
Overweight (≥23–<25 kg/m^2)	176 (24.1%)	20 (18.7%)	156 (25.0%)
Obese (≥25 kg/m^2)	344 (47.1%)	42 (39.3%)	302 (48.4%)
Hypertension, n (%)	453 (62.0%)	59 (55.1%)	394 (63.1%)	0.115
Diabetes, n (%)	242 (33.1%)	29 (27.1%)	213 (34.1%)	0.153
Ischemic heart disease, n (%)	38 (5.2%)	9 (8.4%)	29 (4.6%)	0.105
Stroke, n (%)	43 (5.9%)	5 (4.7%)	38 (6.1%)	0.565
Chronic pain for at least 6 months, n (%)	4 (0.5%)	1 (0.9%)	3 (0.5%)	0.470
Other heart disease, n (%)	14 (1.9%)	3 (2.8%)	11 (1.8%)	0.444
Other lung disease, n (%)	2 (0.3%)	0 (0.0%)	2 (0.3%)	1.000
Chronic illness, n (%)	537 (73.5%)	74 (69.2%)	463 (74.2%)	0.275
Chronic illness (mean ± SD)	1.08±0.84	0.98±0.85	1.10±0.83	0.183

Note:

* Significantly different between groups by independent t-test, Fisher’s exact test, or χ², as appropriate.

Abbreviations: BMI, body mass index; FEV₁, forced expiratory volume in first second; FVC, forced vital capacity; SD, standard deviation.

Figure 1 Study workflow and outcome measurement.

Abbreviations: AO, airflow obstruction; BCSS, Breathlessness, Cough, and Sputum Scale; BD, bronchodilator; FEV₁, forced expiratory volume in the first second; FVC, forced vital capacity; LFQ, Lung Function Questionnaire.

Table 2 Clinical characteristics of subjects with a history of smoking in primary care setting

Characteristics	Total (n=731)	Airflow obstruction: FEV1/FVC <0.7
		Yes (n=107)	No (n=624)	P-value*
Spirometric indices (mean ± SD)
Prebronchodilator
FEV1 (L)	2.6±0.8	2.2±0.7	2.7±0.8	<0.001
FEV1 (% predicted)	106.3±24.6	93.3±25.5	108.5±23.8	<0.001
FEV1/FVC (%)	78.2±9.1	62.8±6.3	80.9±6.4	<0.001
FVC (L)	3.4±0.9	3.4±1.0	3.4±0.9	0.488
FVC (% predicted)	105.4±23.4	112.7±29.7	104.1±22.0	<0.001
FEF 25%–75%	2.5±1.1	1.2±0.7	2.7±1.1	<0.001
FEF 25%–75% (% predicted)	104.0±41.0	58.3±24.5	111.8±38.0	<0.001
Postbronchodilator (n=58)
FEV1 (L)	2.1±0.6	2.1±0.6	2.0±0.6	0.888
FEV1 (% predicted)	89.9±23.0	90.2±22.8	88.9±24.4	0.867
FEV1/FVC (%)	68.0±10.3	65.2±9.4	77.6±6.9	<0.001
FVC (L)	3.0±0.7	3.1±0.7	2.6±0.8	0.026
FVC (% predicted)	98.3±23.3	101.8±20.0	86.2±29.9	0.031
FEF 25%–75%	1.4±0.6	1.3±0.5	1.7±0.9	0.896
FEF 25%–75% (% predicted)	64.6±26.0	59.9±20.2	81.3±36.9	0.701
Pulmonary symptoms (mean ± SD; median, range)
Total BCSS score	0.947±1.121; 1, 0–9	0.963±1.107; 1, 0–6	0.944±1.124; 0, 0–9	0.873
Breathlessness	0.071±0.297; 0, 0–2	0.065±0.284; 0, 0–2	0.072±0.299; 0, 0–2	0.829
Cough	0.378±0.571; 0, 0–3	0.364±0.521; 0, 0–2	0.380±0.579; 0, 0–3	0.798
Sputum	0.498±0.598; 0, 0–4	0.533±0.619; 0, 0–2	0.492±0.594; 0, 0–4	0.515
Outcome measures
Asymptomatic AO (LFQ >18)		5 (4.8%), N=105
Symptomatic AO (LFQ ≤18)		100 (95.2%), N=105
GOLD classification of severity** (N=45)
Mild COPD		27 (60.0%)
Moderate COPD		18 (40.0%)
Severe COPD		0 (0.0%)
Very severe COPD		0 (0.0%)

Notes:

* Significantly different between groups by independent t-test or χ² test, as appropriate.

** Assuming subjects with AO had COPD.

Abbreviations: AO, airflow obstruction; BCSS, Breathlessness, Cough, and Sputum Scale; COPD, chronic obstructive pulmonary disease; FEF, forced expiratory flow; FEV₁, forced expiratory volume in the first second; FVC, forced vital capacity; GOLD, Global Initiative for Chronic Obstructive Lung Disease; LFQ, Lung Function Questionnaire; SD, standard deviation.

Table 3 Factors associated with undiagnosed airflow obstruction or undiagnosed chronic obstructive pulmonary disease by logistic regression

Characteristics	Airflow obstruction: FEV1/FVC <0.7			Airflow obstruction with chronic symptoms: LFQ scored ≤18
	OR	95% CI	P-value	OR	95% CI	P-value
Sociodemographic
Age (years)	1.037	(0.989–1.087)	0.134	1.038	(0.987–1.091)	0.147
Male	1.035	(0.356–3.015)	0.949	1.215	(0.372–3.971)	0.748
Education (university or unknown)			0.803			0.751
Primary or below	1.203	(0.417–3.468)	0.733	1.506	(0.468–4.840)	0.492
Middle school	1.460	(0.489–4.355)	0.497	1.733	(0.519–5.787)	0.372
High school	1.088	(0.340–3.476)	0.887	1.261	(0.350–4.546)	0.723
Occupation (others)			0.729			0.809
Retired	0.711	(0.301–1.678)	0.436	0.747	(0.300–1.858)	0.531
Working	0.840	(0.375–1.881)	0.671	0.865	(0.361–2.072)	0.745
Current smoker	1.191	(0.721–1.968)	0.495	1.288	(0.764–2.173)	0.342
Number of years of smoking	1.044	(1.003–1.087)	0.035	1.051	(1.007–1.096)	0.021
Pack-year	1.000	(0.991–1.010)	0.928	0.999	(0.989–1.010)	0.908
Clinical
Underweight or normal, BMI <23 kg/m^2	1.605	(1.009–2.552)	0.046	1.635	(1.012–2.639)	0.044
Hypertension	0.491	(0.307–0.787)	0.003	0.520	(0.319–0.848)	0.009
Diabetes	0.655	(0.400–1.071)	0.092	0.679	(0.409–1.127)	0.134
Ischemic heart disease	1.625	(0.704–3.755)	0.256	1.716	(0.735–4.004)	0.212
Stroke	0.490	(0.180–1.333)	0.162	0.508	(0.186–1.393)	0.188
Pulmonary symptoms in BCSS score	0.954	(0.781–1.165)	0.642	0.981	(0.799–1.204)	0.853

Notes: Levels in parentheses are reference category of categorical variables. Values shown in bold indicate factors significantly associated with airflow obstruction.

Abbreviations: BCSS, Breathlessness, Cough, and Sputum Scale; BMI, body mass index; CI, confidence interval; FEV₁, forced expiratory volume in the first second; FVC, forced vital capacity; LFQ, Lung Function Questionnaire; OR, odds ratio.