Peak flow diaries in childhood asthma are unreliable.

BACKGROUND: A study was undertaken to investigate the compliance with and accuracy of peak flow diaries in childhood asthma.

METHODS: Forty asthmatic children (5-16 years) were asked to perform peak flow measurements twice daily for 4 weeks by means of an electronic peak flow meter and to record values in a written diary. Patients and parents were unaware that the device stored the peak flow values on a microchip. In random order, half of the patients were only told that the device allowed for more accurate assessment of peak flow while the other half were told that accurate recording of peak flow was important because the results would be used in guiding adjustments to treatment. Data in the written diary (reported data) were compared with those from the electronic diary (actual data).

RESULTS: In the entire study population the mean (SD) actual compliance (77.1 (20.5)%) was much lower than the mean reported compliance (95.7 (9.1)%) (95% CI for difference 12.7% to 24.4%) The percentage of correct peak flow entries decreased from 56% to <50% from the first to the last study week (p<0.04), mainly as a result of an increase in self-invented peak flow entries. Results were comparable for both groups. For incorrect peak flow entries the mean difference between written and electronically recorded entries ranged from -72 to 34 l/min per patient.

CONCLUSIONS: Peak flow diaries kept by asthmatic children are unreliable. Electronic peak flow meters should be used if peak flow monitoring is required in children with asthma.