Can peak expiratory flow measurements reliably identify the presence of airway obstruction and bronchodilator response as assessed by FEV1 in primarycare patients presenting with a persistent cough?

Background-In general practice airway obstruction and the bronchodilator re sponse are usually assessed using peak expiratory flow (PEF) measurements. A study was carried out in patients presenting with persistent cough to inv estigate to what extent PEF measurements are reliable when compared with te sts using forced expiratory volume in one second (FEV1) as the measure of r esponse. Methods-Data (questionnaire, physical examination, spirometry, PEF) were co llected from 240 patients aged 18-75 years, not previously diagnosed with a sthma or chronic obstructive pulmonary disease (COPD), who consulted their general practitioner with cough of at least two weeks duration. The relatio nship between low PEF (PEF < PEFpred - 1.64RSD) and low FEV1 (FEV1 < FEV(1) pred - 1.64RSD) was tested. A positive bronchodilator response after inhali ng 400 mu g salbutamol was defined as an increase in FEV1 of greater than o r equal to 9% predicted and was compared with an absolute increase in PEF w ith cut off values of 40, 60, and 80 l/min and Delta PEF % baseline with cu t off values of 10%, 15%, and 20%. Results-Forty eight patients (20%) had low FEV1, 86 (35.8%) had low PEF, an d 32 (13.3%) had a positive bronchodilator response. Low PEF had a positive predictive value (PPV) for low FEV1 of 46.5% and a negative predictive val ue (NPV) of 95%. Delta PEF of greater than or equal to 10%, greater than or equal to 15%, or greater than or equal to 20% baseline had PPVs of 36%, 52 %, and 67%, respectively, and Delta PEF of greater than or equal to 40, gre ater than or equal to 60, and greater than or equal to 80 l/min in absolute terms had PPVs of 39%, 45%, and 57%, respectively, for Delta FEV1 greater than or equal to 9% predicted; NPVs were high (88-93%). Conclusions-Although PEF measurements can reliably exclude airway obstructi on and bronchodilator response, they are not suitable for use in the assess ment of the bronchodilator response in the diagnostic work up of primary ca re patients with persistent cough. The clinical value of PEF measurements i n the diagnosis of reversible obstructive airway disease should therefore b e re-evaluated.