ORIGINAL ARTICLE
The Clinical Respiratory Journal
Prevalence and predictors of undiagnosed chronic obstructive pulmonary disease in a Norwegian adult general population Sophie Charlotte Hvidsten1, Lene Storesund1, Tore Wentzel-Larsen3, Amund Gulsvik1,2 and Sverre Lehmann1,2 1 Section for Thoracic Medicine, Institute of Medicine, University of Bergen, Bergen, Norway 2 Department of Thoracic Medicine, Haukeland University Hospital, Bergen, Norway 3 Centre for Clinical Research, Haukeland University Hospital, Bergen, Norway
Abstract Objectives: To determine the prevalence and predictors of undiagnosed chronic obstructive pulmonary disease (COPD) in Norway. Methods: An age and gender stratified random sample of all adults aged 47–48 and 71–73 years in Bergen, Norway, were invited. The 3506 participants filled in questionnaires including symptoms of COPD, smoking, socio-economic status, selfrated health and cardiac co-morbidity. Spirometry was performed before and after inhalation of 400 mg of salbutamol. COPD was defined as postbronchodilator forced expiratory volume in 1 s (FEV1) / forced vital capacity (FVC) < 0.7 whereas diagnosed COPD was defined as having received treatment for obstructive lung disease the last year. Results: Three hundred-three persons (9%) were classified as having COPD, and the undiagnosed fraction was 66%. In multiple logistic regression analysis, including multiple imputation, predictors of undiagnosed COPD were absence of COPD symptoms [odds ratio (OR) 6.92, P = 0.001], and self-report of being in good/ excellent health (OR 2.39, P = 0.005). When post-bronchodilator FEV1 was added to the analysis, undiagnosed disease was predicted by pack years [OR 1.21 (1.01– 1.47) per 10 pack-year increase, P = 0.043], and close to normal lung function [OR 1.48 (1.22–1.80) per 10% increase in post-bronchodilator FEV1 % predicted, P < 0.001]. Anthropometrical variables, socio-economic status and cardiac co-morbidity were not associated with having undiagnosed COPD. Conclusion: Two out of three COPD patients in Norway are undiagnosed. Risk factors for being undiagnosed are moderate reduction in lung function, absence of COPD symptoms and self-report of being in good health.
Key words chronic obstructive pulmonary disease – community – epidemiology (pulmonary) – pulmonary function test Correspondence Sverre Lehmann, PhD, Department of Thoracic Medicine, Haukeland University Hospital, N-5021 Bergen, Norway. Tel: +47 55 97 3249 Fax: +47 55 97 5149 email:
[email protected] Received: 26 October 2008 Revision requested: 26 January 2009 Accepted: 27 January 2009 DOI:10.1111/j.1752-699X.2009.00137.x Ethics The study protocol was approved by the Regional Ethics Committee. Conflicts of interest The authors have stated explicitly that there are no conflicts of interest in connection with this article
Please cite this paper as: Hvidsten SC, Storesund L, Wentzel-Larsen T, Gulsvik A and Lehmann S. Prevalence and predictors of undiagnosed chronic obstructive pulmonary disease in a Norwegian adult general population. The Clinical Respiratory Journal 2010; 4: 13–21.
Introduction Chronic obstructive pulmonary disease (COPD) is a major cause of morbidity and mortality throughout the world. Millions of people suffer from this disease and die prematurely because of COPD or its complications. As COPD is preventable and treatable, it is important to identify patients and treat them before they reach the symptomatic and costly stages of the disease. COPD, defined using spirometry, has been consistently underdiagnosed in most continents of the The Clinical Respiratory Journal (2010) • ISSN 1752-6981 © 2009 The Authors. Journal compilation © 2009 Blackwell Publishing Ltd
world (1–9). Results from a Swedish study suggest that half of the affected are lacking the diagnosis (8). To effectively and systematically trace undiagnosed subjects with COPD in a community, knowledge is needed about factors predicting a lack of diagnosis, which has only been reported in two previous papers from the IBERPOC study (9, 10). However, no information on this topic is available from a north European general population. Possible risk factors for undiagnosed COPD could be anthropometrical variables, socio-economic status, cardiac co-morbidity, 13
Undiagnosed COPD in a general population
self-rated health, smoking history and symptoms of COPD (11). The main aims of our study were: (i) to estimate the fraction of subjects with undiagnosed COPD in a middle-aged and elderly cohort with high prevalence of COPD; and (ii) to identify factors associated with an increased risk for having undiagnosed COPD.
Materials and methods Population The Hordaland Homocystein study was conducted during 1992–1993 (12). The target population included all women and men born between 1925–1927 and 1950–1951 living in the municipality of Bergen, 31 December 1992 (n = 11 385). Totally, 7949 (70%) of the invited participated. In 1998–1999 participants who were still alive and living in Bergen (n = 7456) were invited to a follow-up study, the Hordaland Health Study (HUSK). Random samples of 510 persons were drawn from 10 sex–age strata, giving a total of 5100 persons who were invited to participate in the bronchodilatation survey (BDHUSK), a collaborative study between the Norwegian National Health Screening Service, HUSK and the University of Bergen (13). The subjects received a postal questionnaire and an invitation for a reversibility test.
Questionnaires, spirometry and reversibility testing The participants filled in questionnaires including diagnosed obstructive lung disease (14), smoking habits, symptoms of COPD, cardiac co-morbidity, socio-economic status (education and income) and self-rated health. Questions are shown in the Appendix. The questions Q2 (chronic cough) and Q3 (dyspnoea) from the Norwegian Respiratory Questionnaire have been validated against lung function and bronchial reactivity (15), and have also been compared with the British Medical Research Council questionnaire on chronic bronchitis (16, 17). The participants’ heights and weights were measured without shoes and outer garments. Spirometry (18) was performed with a Vitalograph S (Vitalograph, Buckingham, UK) spirometer before, and 15 min after inhalation of 400 mg of salbutamol (19). Through the entire study period the same welltrained technician guided all the reversibility tests and post-bronchodilator measurements were used in accordance with the Global Initiative on Obstructive 14
Hvidsten et al.
Lung Disease (GOLD) classifications (20). Daily calibration including biologic control routines are described in a previously published article (13). The forced expiratory volume in 1 s (FEV1), and the forced vital capacity (FVC) values were corrected to Body Temperature and Pressure Saturated conditions (BTPS), and expressed as percentage of predicted values using normative values from a Norwegian population (21).
Definitions The outcome variable of the study is the categorisation of subjects without COPD, diagnosed COPD and undiagnosed COPD. COPD was defined as postbronchodilator ratio FEV1/FVC < 0.7 (20). Diagnosed COPD was defined by a combined criterion: (i) persons fulfilling the spirometric GOLD criterion for having COPD; and (ii) those who had been treated by a physician or admitted to hospital for obstructive lung disease the last twelve months (14) (exact wording in the Appendix, Q10). Subjects fulfilling only the former criterion were labeled as having undiagnosed COPD. The severity of COPD was classified as mild (FEV1 > 80% predicted), moderate (FEV1 50%–79.9% predicted), severe (49.9%–30% predicted) and very severe COPD (300 000 Self-rated health Fair or poor Good or excellent Lung function GOLD
COPD symptoms* Cardiac co-morbidity Cardiac infarction Angina pectoris
Diagnosed n (%)
Undiagnosed n (%)
Middle-aged (47–48 years) Elderly (71–73 years) Female No overweight 30 kg/m2
11 91 34 51 40 8
(11) (89) (33) (52) (40) (8)
29 172 55 119 62 18
(14) (86) (27) (60) (31) (9)
Never smoker Ex-smoker Current smoker 0 20
15 48 38 15 11 30 42
(15) (48) (38) (15) (11) (31) (43)
17 96 86 17 19 48 100
(9) (48) (43) (9) (10) (26) (54)
0.22
0–11 years >12 years
70 (75) 23 (25)
134 (75) 44 (25)
1.00
4 (4) 28 (27)
14 (7) 49 (24)
0.52
70 (69)
138 (69)
31 (37) 35 (42) 17 (20)
61 (35) 68 (39) 47 (27)
0.56
59 (58) 42 (42)
58 (29) 141 (71)
0.001
Stage I Stage II Stages III–IV Yes
13 55 34 93
64 123 14 95
0.001
Yes Yes
16 (16) 12 (12)
(13) (54) (33) (91)
(32) (61) (7) (47)
26 (13) 21 (11)
Chi-squared test P (two-sided)
0.47 0.29 0.28
0.23
0.001 0.48 0.70
*COPD symptoms: chronic cough, chest wheezing and dyspnoea after climbing two flights or stairs. † Norwegian kroner (1 € = 7, 90 NOK, 27 August 2008). BMI, body mass index; COPD, chronic obstructive pulmonary disease; GOLD, Global Initiative on Obstructive Lung Disease.
that gender, educational level, age, other thoracic diseases and pack years were associated with a previous diagnose. Especially the last two factors were highly related to a COPD diagnosis, with ORs of 3.0 and 5.4 (>30 pack years), respectively. The most likely explanations might be differences in use of spirometry and case-finding among smokers in the two countries. In accordance with a previous Swedish community study (8), the underdiagnosis of COPD was related to The Clinical Respiratory Journal (2010) • ISSN 1752-6981 © 2009 The Authors. Journal compilation © 2009 Blackwell Publishing Ltd
disease severity. This result is not surprising, as persons with mild COPD have few and non-intense airway symptoms, and do therefore not seek a physician. Self-report of health status has been shown to predict survival in several studies of general populations (24, 25). In the present study, however, a selfreport of being in good health independently predicted a non-diagnosed COPD among subjects with spirometric evidence of irreversible airway obstruction. A 17
Undiagnosed COPD in a general population
Hvidsten et al.
Table 3. Risk factors for having undiagnosed chronic obstructive pulmonary disease (COPD) Adjusted odds ratio (95% confidence interval) Anthropometrical variables Gender Men Women (ref) Age Elderly Middle-aged (ref) Body mass index (non-linear) From 20 to 25 kg/m2 From 25 to 30 kg/m2 From 30 to 35 kg/m2 Socio-economic status Marital status Not married Widow(-er)/separated/divorced Married (ref) Education ⱖ12 years 300 000 150 000–300 000
