Review of the literature
2.13 Case finding in COPD
Case finding for COPD is defined as screening by spirometry in “patients who seek medical care for unrelated symptoms and who are at high risk for COPD due to a history of heavy cigarette smoking” (5). This targeting differentiates case finding from spirometry screening in unselected populations, in which the requirements for effective screening are not met (82,83). The use of spirometry for case finding in
COPD remains an area of controversy (84,85). On the evidence available in 2005, case finding was not recommended in a report prepared for the US Government on two grounds; because of lack of effectiveness for spirometry on smoking cessation and lack of availability of effective therapy in airflow obstruction in the absence of symptoms (53). However, case finding has been assessed as relatively cost effective (86). There is however considerable evidence for the feasibility of spirometry in case finding and this is presented in the following sections.
2.13.1 International experience of spirometry screening
A study carried out in 33 general practices and 23 hospital clinics in Japan found undiagnosed airway obstruction by GOLD criteria (Table 2.1) in 281 (27%) of 1,040 subjects considered to be at high risk of COPD (smokers or ex-smokers) (87). Post- spirometry, doctors provided a diagnosis for 70% of those with airway obstruction, asthma in 13% and COPD in 81% (39% classified as mild, 38% as moderate and 19% as severe). Results did not differentiate between GPs and hospital-based physicians.
In a primary care setting in Belgium, 19% of patients who had smoked for at least 10 pack years and were consulting for a non-respiratory complaint without a prior respiratory diagnosis, demonstrated airflow limitation on spirometry by GOLD criteria (Table 2.1). Classification of severity of airflow obstruction was: mild in 34%, moderate in 52% and severe in 14% (88). Another study in Belgium surveyed 3,408 patients between 35 to 70 years consulting a GP over a three-month period (89). 250 patients with known obstructive lung disease, based on current use of bronchodilators were excluded. Among 703 patients with at least one current or recent respiratory symptom tested with spirometry, 18% showed obstructive lung disease using ERS criteria (Table 2.1) and among a random sample of 222 asymptomatic patients, 4% showed obstructive lung disease using ERS criteria. Overall, an estimate of 216 new cases of obstructive lung disease in this population visiting their GP for any reason was made, of whom 42% would not have been recognised on symptom enquiry alone. Although this study was not designed as a prevalence survey, the results would be consistent with a prevalence of 3-5% overall, lower than rates found when smokers are targeted.
A community-based study in a single region in Sweden targeted smokers aged 40 to 55 years. The eligible population was estimated as 19,750 smokers (44). Spirometry was performed on participants recruited in primary health care centres using posters
by trained, experienced nurses. It was repeated with bronchodilator reversibility testing and a steroid reversibility test in those with obstructive lung function. Of 512 smokers tested, 147 (28.7%) had obstructive lung function using the ERS criteria (Table 2.1). Among these smokers with airflow obstruction, a diagnosis of COPD was made in 96% (classified as mild in 85%, moderate in 13% and severe in 3%) and a diagnosis of asthma in 4%. This was not a population prevalence study and those who responded to the invitation for spirometry had more symptoms than smokers in general. Thus the prevalence of COPD of 27% in this sample of smokers
overestimates the frequency of COPD in the total population of smokers.
2.13.2 Australian experience of spirometry screening in general practice
In population of smokers aged over 40 years with at least 10 pack years smoking history in a rural and a suburban practice (n= 355), the prevalence of airway obstruction was 40% using GOLD criteria (90). Severity of obstruction was
classified as mild in 28%, moderate in 8% and severe in 4%. Only 7% of those with obstruction on spirometry had a prior diagnosis of COPD.
2.13.3 Presentation in general practice with symptoms of COPD
Shortness of breath is specified in the GOLD guidelines as a key indicator for
prompting consideration of a diagnosis of COPD (10). Breathlessness was given as a reason for the encounter with a GP in 0.9 per 100 encounters in Australia between 1998 and 2004 (91) in a continuous survey in primary care (92). This would equate to 900,000 encounters per year across Australia. It was the sole reason for 33.8% of these encounters. Where there was no diagnosis, the most frequent investigation was chest radiology (38.2%) with referral for respiratory specialist advice occurring in 2.5%. Of those whose reason for the encounter was a chest symptom or complaint (other than asthma), only 11.2% had a non-radiological investigation, generally spirometry.
2.13.4 Misclassification of COPD in general practice
Case finding requires spirometry and unless a diagnosis is based on spirometry, COPD may be misclassified (93,94). A study in three practices in the UK that did not own a spirometer, used spirometry with bronchodilator reversibility testing to
15% and <200 ml (95). Another study in the UK recruited patients in one practice with a recorded diagnosis of asthma or COPD. These patients underwent spirometry which was assessed by the GP and two specialist physicians. There was a high level of disagreement between the diagnosis recorded and the GP diagnosis based on spirometry (96). Reasons for misclassification other than lack of spirometry or incorrect interpretation could include evaluation of clinical context such as age, sex and smoking status (96,97) and socio-economic factors (97). Similarly high rates of misclassification are likely in Australia, although no data are available.