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In recent years the use of spirometric tests has rapidly increased in primary health care. Practice guidelines assign a central role to spirometry in the management of patients with chronic obstructive pulmonary disease (COPD). 1, 2 As most of these patients are detected and treated in primary care, these guidelines are particularly relevant for general practice. 3, 4 There is some evidence that application of spirometric testing in general practice may reduce the number of undetected cases with chronic respiratory morbidity 5 as well as diagnostic misclassification, 6- 8 which may lead to overall improved respiratory health. 7
The validity (or "reliability") of spirometric tests is a prerequisite for their use as an instrument for diagnosis, monitoring, and management of respiratory disease. 9 Despite their widespread use, little is known about the validity of spirometric tests in the primary care setting. It has been reported that at least one third of tests performed in general practice do not meet the quality criteria which apply to pulmonary function laboratories. 10 Training of practitioners and nurses seems to enhance the quality of testing only temporarily. 10 Four studies have shown that spirometric indices obtained in general practices may be considerably lower than those obtained in laboratories, suggesting insufficient test validity in general practice. 11- 14 However, none of these reports has been peer reviewed and apparent methodological shortcomings justify further studies of this topic. The main objective of the current study was to assess the extent to which the results of spirometric tests performed in general practice correspond with the results of the same tests performed in a certified pulmonary function laboratory.
METHODS
Study design and participants
The study was a repeated cross sectional within subject comparison of spirometric testing in pulmonary function laboratories and general practices. Four pulmonary function laboratories (two in universities, two in general hospitals) and 61 general practices comprising 149 general practitioners (GPs) and 185 practice assistants were involved. (In Dutch general practice the practice assistant is a paramedical professional who has been trained for administrative and patient care related activities.) A priori, we considered the laboratory spirometric tests as "gold standard" 15 measurements.
GPs selected subjects who met the following inclusion criteria: age 30-75 years; current or ex-smoker; diagnosis of COPD as...