Misidentification of airflow obstruction: prevalence and clinical significance in an epidemiological study

Figures & data

Table 1 Group definitions based on the presence of airflow obstruction (AO) according to two methods

Defined groups	Criteria
	Fixed threshold*	LLN**
Definite AO subject	+	+
Misidentified AO subject
Overestimated subject	+	−
Underestimated subject	−	+

Notes:

* Fixed threshold criteria, ratio of FEV₁/FVC <0.7;

** LLN criteria, ratio of FEV₁/FVC less than the fifth percentile of normal.

Abbreviations: FEV₁, forced expiratory volume in first second; FVC, forced vital capacity; LLN, lower limit of normal.

Table 2 Demographic and spirometric data from a total of 554 subjects subgrouped by sex

Characteristics	Total (n=554)	Male (n=229)	Female (n=325)	P-value
Age (years)	52.86±10.06	53.59±10.41	52.35±9.79	0.155
Height (m)	1.59±0.08	1.66±0.07	1.55±0.06	<0.001
Weight (kg)	61.88±11.32	67.24±11.26	58.10±9.74	<0.001
BMI (kg/m^2)	24.33±3.77	24.48±3.53	24.44±3.92	0.431
FVC (L)	2.83±0.83	3.25±0.73	2.53±0.62	0.003
% predicted FVC	86.06±14.74	90.70±16.60	82.79±12.28	<0.001
FEV1 (L)	2.22±0.63	2.61±0.65	1.94±0.42	<0.001
% predicted FEV1	85.50±15.38	89.44±17.75	82.73±12.78	<0.001
Ratio of FEV1/FVC	0.82±0.07	0.80±0.08	0.83±0.06	<0.001

Note: Results are expressed as means ± SD unless otherwise indicated.

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

Table 3 Frequency by group definition according to the presence of airflow obstruction (AO) based on two methods

Classification of subjects	n (%)
No AO subjects	493 (89.0)
Definite AO subjects	30 (5.4)
Misidentified AO subjects	31 (5.6)
Underestimated subjects	31 (5.6)
Overestimated subjects	0 (0.0)

Table 4 Classification of underestimated subjects (n=31)

Classification	n (%)
Group I: non-ills	4 (12.9)
Group II: clinical AO diseases	7 (22.6)
COPD	3
Asthma	4
Group III: undetermined subjects	20 (64.5)
Smokers ≥5 pack-years	5
Chronic rhinitis symptoms	2
Chronic phlegm	1
Breathlessness on walking	1
Comorbidity	1
Non-smokers or smokers <5 pack-years	15
Chronic rhinitis	9
Breathlessness on walking	4
Comorbidity	2

Abbreviations: AO, airflow obstruction; COPD, chronic obstructive pulmonary disease.

Table 5 The clinical diagnosis of airflow obstruction in the underestimated subjects

No.	Age (sex)	Diagnosis	Clinical evidence
1	68 (M)	COPD (post-TB)	Previous physician-diagnosed pulmonary tuberculosis. Active smokers (10.4 pack-years). Diffuse pulmonary hyperinflation with flattened diaphragms on chest radiograph (compatible with COPD) without tuberculosis scar.
2	65 (M)	COPD	Ex-smoker (6.4 pack-years). Diffuse pulmonary hyperinflation with flattened diaphragms on chest radiograph (compatible with COPD).
3	52 (M)	COPD (post-TB)	Previous physician-diagnosed pulmonary tuberculosis. Ex-smoker (2.1 pack-years). Diffuse pulmonary hyperinflation with flattened diaphragms on chest radiograph (compatible with COPD) with post-tuberculosis bronchiectasis on both upper lobes.
4	48 (F)	Asthma	Current wheezer, non-smoker, physician-diagnosed allergic rhinitis for 4 years, skin test positive for aeroallergen, non-smoker, family history of atopy was positive for asthma.
5	54 (F)	Asthma	Current wheezer, physician-diagnosed allergic rhinitis for 4 years and asthma for a year, skin test was positive for aeroallergen, family history of atopy was positive for asthma, ex-smoker (20 pack-years).
6	45 (F)	Asthma	Current wheezer, physician-diagnosed allergic rhinitis and asthma for 20 years, skin test was positive for aeroallergen, non-smoker.
7	50 (F)	Asthma	Current wheezer, physician-diagnosed allergic rhinitis for 30 years and asthma for 20 years, skin prick test was positive, non-smoker.

Abbreviations: M, male; F, female; COPD, chronic obstructive pulmonary disease; TB, tuberculosis; No. subject number.

Figure 1 Age distribution of entire study population based on sex.