Determinants of spirometry use and accuracy of COPD diagnosis in primary care.

Background: It is unclear if primary care physicians are following guidelines or using other patient characteristics and factors to determine when to perform spirometry in patients at risk for COPD. It is also unclear to what degree a diagnosis of COPD is accurately reflected by spirometry results.

Objectives: To examine characteristics associated with use of spirometry in primary care for patients with increased risk for COPD and to determine the accuracy of COPD diagnosis in patients with spirometry.

Design: Retrospective cohort study.

Subjects: A cohort that met the following criteria was identified: ≥35 years of age; ≥ 2 primary care visits in internal medicine clinic in 2007; at least one respiratory or smoking cessation medication, or diagnosis of COPD or shortness of breath or dyspnea in 2007.

Main Measures: Medical records of all primary care physician visits prior to the time of inclusion in 2007 were reviewed. Data on patient demographics, co-morbidities, respiratory medication use, presence of symptoms, history of tobacco use, and pulmonary function tests were extracted.

Key Results: A total 1052 patients were identified. Dyspnea on exertion (Adjusted odds ratio (AOR) 1.52 [95% CI 1.06-2.18]) and chronic cough (AOR 1.71 [1.07-2.72]) were the only chronic symptoms associated with use of spirometry. Current (AOR 1.54 [0.99-2.40]) or past smoking (AOR 1.09 [0.72-1.65]) status were not associated with use of spirometry. Of the 159 patients with a diagnosis of COPD, 93 (58.5%) met GOLD criteria and 81(50.9%) met lower limit of normal (LLN) criteria for COPD.

Conclusion: Clinicians use spirometry more often among patients with symptoms suggestive of COPD but not more often among patients with current or past tobacco use. For patients who had a spirometry and a diagnosis of COPD, primary care physicians were accurate in their diagnosis only half of the time.