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Office Spirometry Significantly Improves Early Detection of COPD in General Practice^*

The DIDASCO Study

^* From the Departments of General Practice (Drs. Buffels, Degryse, and Heyrman) and Pulmonology (Dr. Decramer), Katholieke Universiteit, Leuven, Belgium.

Correspondence to: Johan Buffels, MD, Academisch Centrum voor Huisartsgeneeskunde Kapucijnenvoer 33 Blok J B-3000 Leuven, Belgium; e-mail: johan.buffels{at}coditel.net

	Abstract

TOP Abstract Introduction Materials and Methods Results Discussion Conclusion References

 
Study objectives: To determine if spirometry is essential for the early detection of COPD in general practice, compared to the screening value of a short questionnaire.

Methods: A prospective survey of the population aged 35 to 70 years visiting their general practitioner (GP) during a 12-week period, using a questionnaire on symptoms of obstructive lung disease (OLD). Spirometry was performed in all participants with positive answers and in a 10% random sample from the group without complaints. Twenty GPs were provided with a hand-held spirometer, and received training in performance and interpretation of lung function tests. All 35- to 70-year-old patients (n = 3,408) were screened for current use of bronchodilators. The subgroup receiving bronchodilators (n = 250, 7%) was assumed to have OLD, and was excluded. Airflow obstruction was defined according to the European Respiratory Society standards.

Results: The positive predictive power of the questionnaire was low (sensitivity, 58%; specificity, 78%; likelihood ratio, 2.6). One hundred twenty-six cases of formerly unknown OLD were detected in the group of patients with complaints, vs an extrapolated number of 90 in the group without complaints. Despite a negative predictive value of 95% for the questionnaire used, 42% of the newly diagnosed cases of OLD would not have been detected without spirometry.

Conclusions: The use of a spirometer is mandatory if early stages of OLD are to be detected in general practice. Screening for airflow obstruction almost doubles the number of known patients with OLD.

Key Words: asthma • COPD • diagnosis • family practice • spirometry

	Introduction

TOP Abstract Introduction Materials and Methods Results Discussion Conclusion References

 
Current consensus guidelines, such as the Global Initiative for Chronic Obstructive Lung Disease (GOLD) program¹ emphasize the importance of early detection of the disease, even at a preclinical stage. It is commonly accepted that spirometry is the "gold standard" in the diagnosis of COPD.¹² Until now, only a few studies³ have been performed on the diagnosis of COPD in general practice, although it appears quite probable that the majority of the patients with unidentified COPD first consult with a general practitioner (GP).

Modern lightweight spirometry instruments that can be wired into a computer are now available. This makes spirometry technically feasible at the primary care level. Some authors⁴ state that mild and even moderate COPD can occur without complaints or symptoms. Moreover, there seems to be a weak correlation between the severity of the complaints and the severity of airway obstruction.⁵ In addition, there is a certain underreporting of complaints in subjects with obstructive lung disease (OLD), particularly shortness of breath.⁶⁷⁸ Few data are available about the actual incidence and prevalence of the early stages of this disease.

A major differential diagnosis of COPD is asthma. It is important to make a distinction between asthma and COPD, since the guidelines for assessment and management are quite different for the two diseases.¹⁹ The aim of the DIDASCO (Differential Diagnosis Between Asthma and COPD) project was to study the ability of general practitioners to detect early stages of chronic OLD, and to make a distinction between asthma and COPD using relatively simple means.

The first step in this larger project was to determine the accuracy of the results of office spirometry performed by GPs. Consequently, an algorithm was developed to determine whether airflow obstruction could be diagnosed most effectively by routine spirometry in the target population or by a questionnaire followed by spirometry in the patients with complaints. In this article, we report these results.

	Materials and Methods

TOP Abstract Introduction Materials and Methods Results Discussion Conclusion References

 
General Design of the Study
The target population for early detection of COPD was defined as the age group from 35 to 70 years. The participating GPs were asked to screen every patient in this age group attending clinic at least once during 12 successive weeks for use of bronchodilators and/or inhaled steroids, since they were assumed to have known asthma or COPD. All other subjects were to complete a short questionnaire pointing to signs and symptoms of OLD (Table 1 ). Patients with at least one positive answer were given an appointment for a spirometry within 1 week. In the group without complaints, an electronic randomization procedure assigned 10% to a control group, which underwent a spirometry within 1 month of the questionnaire being completed. The study flow diagram is shown in Figure 1 .

View larger version (25K): [in this window] [in a new window] [Download PPT slide]   Figure 1. Study flow diagram.

Airflow obstruction was defined according to the European Respiratory Society standards for optimal management of COPD.¹⁰ Values of the FEV₁/FVC ratio < 88.5% of the predicted value for men, and < 89.3% of the predicted value for women were considered to be consistent with airflow obstruction.

Questionnaire
The questionnaire was short and simple, because the screening took place during the normal consultation activity of the GPs, including their home visits. The version that was used (Table 1) was derived from the European Community Respiratory Health Study questionnaire.¹¹ The patients were asked if they were troubled by one of the following complaints either currently or during the past year: a cough lasting for at least 2 weeks, breathing difficulties during mild exercise or during the night, wheezing, or any kind of nasal allergy or hay fever. They were also asked if they ever visited the doctor for wheezing or a long-lasting cough. If one of these questions received a positive answer, the patients were asked to undergo spirometry.

The questionnaire focused on signs and symptoms of possible OLD, not on risk factors. There was no separate question about cigarette smoking, because there is existing evidence that spirometric testing should be offered to all current smokers > 45 years of age, and GPs usually already know the smoking habits of their patients. An extra question regarding sputum production might have added to the sensitivity of the questionnaire. However, the European Community Respiratory Health Study¹¹ found a high correlation coefficient between the factors cough and phlegm, and it was important to make the questionnaire as concise as possible.

Accuracy of the Spirometric Values
The accuracy of the spirometric values obtained by the participating GP was examined as follows. In a separate event, each GP invited a patient with airflow obstruction to a joint meeting in the lung function laboratory of the University Hospital in Leuven. Each of the patients underwent five successive spirometric tests: four tests by different GPs, using their own spirometer, and one test performed by a professional laboratory technician with his usual equipment. A reliability analysis was performed using the generalizability theory (unpublished data).

Differentiation Between Asthma and COPD
A second part of the study focused on the ability of GPs to distinguish between asthma and COPD. Every patient with newly found airway obstruction was offered a bronchodilator reversibility test within 1 week of the initial spirometry. Reversibility was defined as an increase of at least 12% for the FEV₁ percentage of the predicted value or 200 mL after administration of 400 µg salbutamol (or 80 mg ipratropium bromide for patients at risk). Patients with reversible OLD were considered to have asthma. Patients who failed to show reversible airway obstruction after the use of bronchodilators were asked to undergo a steroid challenge test by inhalation for a period of 12 weeks. At the end of that period, lung function tests were repeated. The results of this trial will be presented in a separate article.

	Results

TOP Abstract Introduction Materials and Methods Results Discussion Conclusion References

 
Demographic Data
During a period of 12 weeks from April to July 1999, 22 GPs applied the case-finding algorithm to all of their visiting patients (n = 3,408) aged 35 to 70 years. Two hundred fifty patients (7.3%) used bronchodilators and/or inhaled steroids, and were assumed to have asthma or COPD. The other 3,158 subjects were submitted to the short questionnaire. Seven hundred twenty-eight responders (23%) gave at least one positive answer, indicating that they had a higher probability of OLD. From this group, 703 spirometric tests were obtained. Consequently, 126 cases of formerly unknown OLD were identified, ie, 18% of the group with complaints. Ten percent of the 2,430 remaining patients without complaints were selected at random to form a control group. From the 222 spirometric tests performed in this group, nine results (4%) revealed airflow obstruction. Extrapolation to the total group refers to 90 expected new cases. In total, approximately 216 new cases were detected. This represents 7.4% of the population aged 35 to 70 years who spontaneously visit their GP.

The newly diagnosed cases with airflow obstruction were spread equally over the different age categories, while patients with known OLD were more obviously present in the older age groups. Fifty-two percent of the population studied were women. In the group with newly diagnosed OLD, 45% were women, whereas in the group with known obstructive airway disease only 15% were women.

As expected, the percentage of smokers in the group with newly diagnosed OLD (48%) exceeds by far the number of smokers in the group with normal lung function test results (28%). A less important difference was seen for the number of ex-smokers (23% vs 19%).

In the population with formerly unknown airway obstruction, the mean FEV₁ was 2.57 L (SD 0.75), and the mean FEV₁ predicted was 74.09% (SD 18.2). Table 2 shows a comparison between the groups with and without complaints. Table 3 shows the staging of the newly found airflow obstruction. A large majority of subjects presented with mild-to-moderate airflow obstruction: 90% of these patients had a FEV₁ > 50% of the predicted value. Only one subject had a FEV₁ of < 30% predicted at the time of detection.

	Discussion

TOP Abstract Introduction Materials and Methods Results Discussion Conclusion References

 
The present study demonstrates that spirometry in general practice is feasible and sufficiently accurate. In the target population aged 35 to 70 years, we found 7.4% of patients with formerly unknown OLD. Of these patients, 42% would not have been found without the screening with spirometry. The degree of airflow obstruction was mild to moderate.

Epidemiologic Considerations
In the DIDASCO project, the GPs managed to screen all of their visiting patients of the selected age group for this prospective survey. Although this study was not designed as a population survey, some epidemiologic extrapolations can be attempted, in the form of rough estimations.

Belgian primary health care has no patient census list. Prior evidence has shown that the number of patients visiting the GP at least once during a 12-week period equals a 60% fraction of the yearly patient contact group (YCG). This total YCG is relatively stable in a single practice and is equivalent to approximately 70% of the total practice population.¹²¹³

During the 12 registration weeks, 250 patients in 18 practices were found to use bronchodilators. After simple linear extrapolation for the YCG, this should refer to 416 cases with known OLD. However, it might be argued that the majority of the population with asthma or COPD will visit the GP within a 12-week period anyway, either for follow-up of the disease and prescriptions, or for intercurrent diseases or exacerbations. Using this "minimal hypothesis," the total number of known cases with airway obstruction would hardly exceed the initial 250 cases. However, several studies⁷ report a low compliance to therapy in a significant number of patients with obstructive airway disease, especially in the group with mild signs and symptoms. This could lead to underreporting in the present study, even in the "maximal hypothesis."

On the denominator side, a total number of 3,408 patients from 35 to 70 years old underwent screening. Extrapolation to the YCG leads to 5,680 subjects, or a total practice population of 8,114 persons for this age group. The prevalence of known airway obstruction in this study can be calculated as from 250 to 416 cases for the total population of 8,114, or from 30 to and 51 cases per 1,000. This is quite comparable with prevalence estimates obtained in other studies eg, the United States Third National Health & Nutrition Examination Survey¹⁴ and the Confronting COPD International Survey.¹⁵

The number of patients that can be found during 1 year using the active screening strategy adopted in this study is estimated to total 360 cases (extrapolation to the YCG). Comparing this figure with the number of cases with known airway disease, we conclude that there is about one patient with unknown asthma or COPD for every known patient in primary care (360 cases vs 250 to 416 estimated cases). These findings confirm the conclusions of earlier studies^14151617 that OLD in general practice can be compared to an iceberg: only the tip is visible. The combined prevalence of new and known cases of OLD leads to an estimated global prevalence between 75 and 96 per 1,000. Of course, as we stated above, several causes of bias must be taken into account since this was not a population study.

The figures of newly diagnosed obstructive airway disease in the present study are lower than those of a Dutch population study, the Detection, Intervention and Monitoring of COPD and Asthma project.¹⁶ It should be noted that the design of this included several measurements of the lung function, while the DIDASCO study is based essentially on only one spirometry as a screening tool. Probably a larger number of asthma patients can be detected if spirometry is repeated during a period of several months. This could be considered as a methodologic weakness of the study design, but the primary focus was rather early detection of COPD.

Furthermore, the DIDASCO study is not to be considered as a study about the broad general population. Only patients visiting a GP were screened. It is difficult to estimate the differences between this selection and the general population. More patients with general morbidity will probably have been included in the present study. However, patients with low self-care and "low health-care consumer profile" will be less represented. In comparison to a Polish study¹⁸ on early detection of COPD, we found lower rates for OLD; this can be explained by the different inclusion criteria because the Polish study focused on smokers only.

Is Early Detection of Obstructive Airway Disease Indicated?
Early detection of a disease only makes sense if an appropriate treatment is available.¹⁹ For early stages of COPD, the only approach that has proven useful on modifying the course of the disease is smoking cessation. However, the usefulness of medical treatment for mild and early asthma is well documented. Early detection of obstructive airway disease should be promoted if an important fraction of the newly diagnosed cases appears to be asthma. Moreover, general measures such as avoidance of other etiologic factors, physiotherapy, anti-infectious prophylaxis, and adequate physical activity can be promoted earlier in the course of COPD.¹²⁰

	Conclusion

TOP Abstract Introduction Materials and Methods Results Discussion Conclusion References

 
The present study shows that spirometry in general practice is feasible provided that the GPs are instructed and trained in the use of a hand-held spirometer. The accuracy of their measurements was found to be highly acceptable. The GPs were able to incorporate spirometry in their daily routines.

If early detection of OLD is to be realized in general practice, the use of a spirometer is essential. Detection based on the use of a questionnaire appeared to be insufficient.

These conclusions could change the policy for early detection of OLD.^115162122 Efforts should be made to make hand-held spirometers available in primary care, and to provide GPs with skills and training in this specific domain. Programs for routine office spirometry in general practice are to be encouraged.

	Acknowledgements

 
We thank the GPs who participated in the registration: P. Bastaerts, M. Biervliet, P. Boeykens, B. Bruynbroeck, L. De Moor, P. De Ridder, A.M. Deleenheer, L. Frisch, R. Gors, M. Joossens, H. Marechal, L. Martens, C. Micholt, G. Opsomer, W. Renier, A. Roex, M. Roex, I. Tambuyzer, P. Tarpataki, D. Van Achter, D. Van de Sijpe, and L. Van Parijs. We are very grateful to P. Vermeire, C. Van Weel, and C. P. Van Schayck for reviewing the study design.

	Footnotes

 
Abbreviations: DIDASCO = Differential Diagnosis Between Asthma and COPD; GOLD = Global Initiative for Chronic Obstructive Lung Disease; GP = general practitioner; OLD = obstructive lung disease; YCG = yearly patient contact group

Financial support was provided by Boehringer Ingelheim Belgium.

Received for publication July 24, 2003. Accepted for publication November 24, 2003.

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