Objectives: To evaluate the adequacy of control of asthma in patients attending a general practice; and to examine the validity of peak expiratory flow rate (PEFR) as an index of asthma severity in the context of general practice.
Design: Short-term cohort study using indices derived from two weeks of peak flow monitoring to evaluate asthma control.
Participants: Known and newly diagnosed asthmatics aged six years or more who presented during the study period for any reason. They were enrolled if baseline forced expiratory volume in one second (FEV1) increased by 10% or more after the administration of nebulised salbutamol. Children under the age of 12 years with no initial response to bronchodilator were included if an exercise test performed on another day was positive.
Outcome measures: Peak flow criteria for "mild asthma" in the Asthma Management Plan, 1989 (Med J Aust 1989; 151: 650-653) were used as the initial definition of "adequate control". The definition of "adequate control" was modified to variability less than 20% and a minimum PEFR of 50% or more of mean predicted value.
Results: There was no association between variability and maximum PEFR, but variability was strongly correlated with minimum PEFR (R = -0.60; P < 0.0005). Asthma was adequately controlled in 68% of the participants.
Conclusion: Current guidelines with respect to the peak flow indices used in the classification of the severity of asthma need to be re-evaluated and probably changed for application in general practice.