Mini-Wright peak flow meters are reliable after 5 years use

In studies with a long-term follow-up, peak expiratory flow (PEF) meters are often used to assess bronchial obstruction. The question arises whether data obtained with these frequently used meters are still reliable after several years of use, and whether the old meters should be renewed after a certain period. In the present study, we tested the reliability of PEF values measured with mini-Wright PEF meters that had been used frequently for 5 yrs. The values obtained with these meters were compared with values measured with identical but new meters, in 50 patients with obstructive airways disease. Though statistically significant, there was no clinically significant difference in mean PEF measured with the old and new meters in most patients (mean difference 10.2 L.min-1). However, on an individual basis, the differences between old and new meters could be large (upper and lower limits of agreement (mean +/- 2 SD) being 63.6 and -43.2 L.min-1, respectively). We conclude that mean peak expiratory flow values measured with frequently used mini-Wright peak expiratory flow meters are still reliable after 5 yrs. In long-term studies, renewal of peak expiratory flow meters should be restricted to cases of obvious malfunction.