Chronic obstructive pulmonary disease (COPD) is a common disease usually treated in general practice, especially in the early stages.1 The recently published British Thoracic Society guidelines encourage a systematic approach to the management of COPD as is widely used in asthma.2 Lung function measurements are regarded as central to the correct implementation of the guidelines.The guidelines are unequivocal in advising the use of forced expiratory volume in one second (FEV₁) rather than peak expiratory flow (PEF) in the management of COPD: “. . . in COPD the relationship between PEF and FEV₁ is poor and it is not possible to predict FEV₁ from the PEF or vice versa.” This is a key issue for GPs who have to decide now whether or not to purchase a spirometer, and whether they have the organisational capacity to cope with the maintenance, calibration, and interpretation demands of modern spirometers.

We have investigated the literature examining the relationship between FEV₁ and PEF and exploring their use in COPD. We have been unable to find substantive evidence to support the statement in the BTS guidelines regarding the superiority of FEV₁ over PEF. The only citation among the 171 references offered in the guidelines to support their position is a paper by Kelly and Gibson.3 In fact, Kelly and …