Quality of routine spirometry tests in Dutch general practices

Setting and spirometry tests

Using a central database, analysis was carried out of all routine care spirometry tests (either a prebronchodilator test alone or a full reversibility test consisting of a prebronchodilator and a postbronchodilator test) that had been submitted by GPs from March 2003 to August 2005. Each of the 15 general practices involved owns a PC-based spirometer and software (SpiroPerfect™, Welch Allyn, Delft, the Netherlands). The hospital's pulmonary laboratory service has direct access to the tests submitted by GPs. Spirometry training and support has been offered to GPs (with a focus on test interpretation), practice nurses, and practice assistants (with a focus on performing tests) once or twice a year since the late 1990s.

After online submission of results to the central database, the quality of spirometry tests is first judged by a pulmonary function technician. Based on the 1994 American Thoracic Society spirometry guideline,6 several spirometry quality markers were derived for every test submitted by the general practices. (It was decided not to use the more recent 2005 guideline10 because it had not yet been published at the time when the spirometry tests were performed.) Box 1 shows the test quality markers as extracted from the 1994 American Thoracic Society spirometry guideline, and for each marker whether or not it could be included in the study analysis of general practice spirometry test quality. Figure 1 shows examples of unacceptable blows for markers that can be judged from the flow–volume curve. After the pulmonary function technician's quality assessment, each test is diagnostically assessed by one of the hospital's chest physicians, who records the presence and/or severity of airflow obstruction, reversibility after bronchodilation, and a possible restrictive pattern. The combined results of the quality assessment and the diagnostic assessment of each test are reported back to the general practice.

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Figure 1

Examples of unacceptable spirometry test quality markers as read from the flow–volume curve.

Statistical analysis

For repeated measurements, the same patient could contribute multiple spirometry tests. For the analysis of spirometry test quality, only the prebronchodilator tests of patients aged ≥12 years were used. After analysis of the test quality markers for the total study population, 675 patients (62%) could be stratified according to the severity of their airflow obstruction as judged by a chest physician. When the chest physician had judged that obstruction was present but had not indicated the severity (12% of all patients with obstruction), the cut-off values from the Global Initiative for Chronic Obstructive Lung Disease guideline11 were used to categorise severity: forced expiratory volume in 1 second (FEV₁) % predicted >80% for mild; 50–80% for moderate; and <50% for severe and very severe obstruction. European Coal and Steel Community reference equations were used to calculate FEV₁ predicted values.12 Patient characteristics were compared between severity subgroups using χ² tests and analysis of variance. Multivariable logistic regression analysis was used to explore associations between spirometry test quality markers and sex, age, and severity of obstruction. The odds ratio (OR) estimates from the logistic regression models express the (adjusted) risk for an inadequate test quality marker to be present. Statistical tests were two-sided, and P<0.05 was considered statistically significant.

General practices

Spirometry tests had been submitted by all 15 general practices comprising 49 GPs (mean number of GPs per practice = 3.3, range = 1–5). Two practices (13%) had implemented spirometry <1 year ago, three practices for 1–2 years ago, and the remaining practices ≥2 years ago. A mean of four spirometry tests (standard deviation [SD] = 2) were performed per week. Spirometry was administered by a practice assistant in 12 practices, by a practice nurse in six practices, and by a GP in two practices (in some practices, more than one type of healthcare professional administered spirometry).

Patients

Mean age of the study population (n = 1091) was 53.4 (SD 16.9) years (Table 1), and mean FEV₁ % predicted was 82.5% (SD 21.0%); 143 patients (13.1%) contributed two spirometry tests to the database on two different dates, 18 patients (1.7%) contributed three or more tests. Bronchodilator reversibility testing was performed in 92.5% of all the patients involved.

Indications for spirometry as reported by the GPs were: (re)assessment of previous diagnosis of chronic airways disease, including tests to assess possible exacerbations (42%); diagnostic assessment without prior diagnosis of chronic airways disease (35%); periodic monitoring of lung function (13%); evaluation of diagnostic prednisolone test (6%); and screening of smokers (4%).

Acceptability and reproducibility of spirometry tests

A total of 1271 prebronchodilator tests comprising 3968 forced expiratory manoeuvres (blows) were available for analysis. Mean number of blows per test was 3.1 (range = 1–9) and 97.8% (95% confidence interval [CI] = 97.0 to 98.6) of all tests consisted of three or more blows; 38.8% (95% CI = 36.0 to 41.6) of the tests met the acceptability as well as the reproducibility criteria (Table 2). The proportion of tests that met all five assessed acceptability markers was 43.3% (95% CI = 40.2 to 45.8; Table 3).

In 37.6% of all tests, one marker was judged by the pulmonary function technician to be unacceptable, two markers in 11.4%, three markers in 5.2%, and four or five markers in 2.5%. With 60.6%, forced expiratory time was the marker with the lowest rate of acceptability. The average forced expiratory time was 7.6 seconds (SD 3.9 seconds). Adequacy of the other acceptability markers ranged from 80.5% for duration of the forced expiration to 92.7% for steep initial incline of the flow–volume curve (Table 3).

Associations between acceptability markers and patient characteristics

Age, sex, and severity of obstruction were associated with one or more of the acceptability markers (Table 4). Compared with males, females had a higher ‘risk’ of unacceptable blows for two markers, that is, duration of forced expiration (OR = 1.57, 95% CI = 1.15 to 2.14) and initial incline to peak flow (OR = 3.00, 95% CI = 1.50 to 6.00). In one or more of the older age groups, the risk of an unacceptable marker increased for initial incline to peak flow, sharpness of peak, and course of forced expiration. The presence of obstruction showed an inverse relationship with the initial incline to peak flow, sharpness of peak, course of forced expiration, and duration of the forced expiration (Table 4). When the fully acceptable tests were offset against the tests with one or more markers that indicated unacceptability, females showed a higher risk of test unacceptability (OR = 1.67, 95% CI = 1.23 to 2.35; not shown in Table 4).

Summary of main findings

This study aimed to establish the quality of general practice spirometry tests outside a typical research setting, and explored whether spirometry test quality was associated with patients' sex and age, and the presence of obstruction in patients tested in general practice. It was found that 39% of all tests performed in the general practices met the combined set of acceptability and reproducibility markers as derived from the 1994 American Thoracic Society spirometry guideline. Too short forced expiratory time was the marker with the lowest rate of acceptability (60.6%). Several associations were observed between test acceptability markers and sex, age, and presence or severity of airflow obstruction.

Strengths and limitations of the study

Particular strengths of this study are that all the tests in the spirometry database were obtained from ‘regular’ (that is, non-academic) general practices, and that they were performed as a part of routine testing in daily patient care. Compared to Dutch national figures, the general practices in the present study were mostly group practices with three or more GPs (56% versus 13% nationally), had slightly less experience with spirometry (6 versus 7 years), and performed a similar number of spirometry tests per month (16 versus 17 tests/month).13^,14 A weakness of the study may be that all practices involved in the evaluation participated in the working agreement with the local hospital, which may limit the external validity of the findings; it is not possible to tell from this study how practices that have no expert support for their spirometry would perform.

Despite these shortcomings, the present findings contribute to the current knowledge regarding spirometry test quality in primary care, and identify points of impact for quality improvement.

Comparison with existing literature

Too short forced expiratory times and early termination of expiratory manoeuvres have previously been recognised as one of the main deficiencies of spirometry in general,15^,16 and of primary care spirometry in particular.9^,17 In this study, associations were observed between several spirometry acceptability markers and both presence of airflow obstruction and older age. An association between older age and worse spirometry test performance has been reported previously, and is likely to be explained by cognitive impairment in older people.9^,18^–20 Contrary to previous reports in which male sex was associated with poorer reproducibility of FEV₁,19 the present study showed an association of female sex with test inadequacy for two acceptability markers: forced expiratory time and initial incline to peak flow. The explanation may be that females feel more embarrassed than males while performing forced expiratory manoeuvres because of the possibility of leaking urine.13

Differences between previous studies and the present observations may be caused by several factors. Different levels of spirometry training among the primary care professionals who administer the tests is certainly one of these factors.7 The achievements of the general practices in the current study contrast with those previously reported from a New Zealand study, which showed far more dramatic results: 3–13% percent of all tests were acceptable and reproducible, with almost the same set of criteria as used in the present study.9

A comparison with the studies reported from pulmonary function laboratories shows that in research as well as in routine care the proportion of reproducible tests is generally at least 90% (Appendix 1). It is doubtful whether primary care professionals will ever be able to approach this performance level. Apart from limited training and quality assurance activities, lack of experience and routine are likely to be important factors in the high rate of low-quality spirometry tests observed in general practice.7^,21 On the other hand, it is currently unclear what the actual impact of inadequate spirometry tests on diagnosis and patient management is. The current authors have previously demonstrated that, compared with measurements from pulmonary function laboratories in the same patients, FEV₁ and forced vital capacity as measured by trained general practice staff do not necessarily result in differences that are relevant in general practice.22 This suggests that an important proportion of spirometry tests that are technically ‘imperfect’ according to the stringent international test criteria6^,10 may still provide the GP with useful results on which to base diagnosis and patient management. In the authors' view, obtaining sufficiently reliable and clinically meaningful spirometry tests — not necessarily perfect tests — is what primary care should be striving for.

If spirometry is to be widely available in primary care, the logistics of training and maintaining standards among large numbers of primary care physicians and nurses requires condensed and pragmatic training programmes. However, training alone will not guarantee sufficient test quality in the longer term.9^,19 A recent report from the UK concluded that the quality of primary care spirometry was unsatisfactory, and its authors suggested that remote reporting of tests may be a means of establishing adequate spirometry.23 Studies conducted in specialised,16^,18^,19^,24^,25 as well as in primary care settings9^,26 suggest that quality-assurance initiatives are able to improve spirometry test quality.

Implications for clinical practice

In this real-life study it was found that quality aspects of spirometry tests in Dutch general practice were better than those previously reported from primary care research settings, but test quality does not approach the levels observed in pulmonary function laboratories. Duration of forced expiration is the quality marker with the highest rate of inadequacy. Primary care professionals who administer spirometry to their patients should be aware of the patient characteristics that may diminish the quality of their spirometry tests. Implementation of contemporary and efficient modes of training and quality assurance feedback may raise and maintain the standards of primary care spirometry.