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Current clinical guideline definitions of airflow obstruction and COPD overdiagnosis in primary care

Depts of ¹ General Practice, and ⁶ Lung Diseases, Radboud University Nijmegen Medical Centre, Nijmegen, ² General Practice Laboratory Foundation Etten-Leur/Breda, Etten-Leur, ³ General Practice Laboratory East, Velp, ⁴ Eindhoven Diagnostic Centre, Eindhoven, Eindhoven, and ⁵ Dept of Lung Diseases, Franciscus Hospital, Roosendaal, The Netherlands.

CORRESPONDENCE: T. R. J. Schermer, Dept of General Practice - 117/HAG, Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands. Fax: 31 243541862. E-mail: T.Schermer{at}hag.umcn.nl

Keywords: Chronic obstructive pulmonary disease, diagnostics, lung function measurements, primary care

Received: December 18, 2007
Accepted May 28, 2008

The aim of the present study was to establish the agreement between two recommended definitions of airflow obstruction in symptomatic adults referred for spirometry by their general practitioner, and investigate how rates of airflow obstruction change when pre-bronchodilator instead of post-bronchodilator spirometry is performed.

The diagnostic spirometric results of 14,056 adults with respiratory obstruction were analysed. Differences in interpretation between a fixed 0.70 forced expiratory volume in one second (FEV₁)/forced vital capacity (FVC) cut-off point and a sex- and age-specific lower limit of normal cut-off point for this ratio were investigated.

Of the subjects, 53% were female and 69% were current or ex-smokers. The mean post-bronchodilator FEV₁/FVC was 0.73 in males and 0.78 in females. The sensitivity of the fixed relative to the lower limit of normal cut-off point definition was 97.9%, with a specificity of 91.2%, positive predictive value of 72.0% and negative predictive value of 99.5%. For the subgroup of current or ex-smokers aged 50 yrs, these values were 100, 82.0, 69.2 and 100%, respectively. The proportion of false positive diagnoses using the fixed cut-off point increased with age. The positive predictive value of pre-bronchodilator airflow obstruction was 74.7% among current or ex-smokers aged 50 yrs.

The current clinical guideline-recommended fixed 0.70 forced expiratory volume in one second/forced vital capacity cut-off point leads to substantial overdiagnosis of obstruction in middle-aged and elderly patients in primary care. Using pre-bronchodilator spirometry leads to a high rate of false positive interpretations of obstruction in primary care.

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