Peak flow diaries in childhood asthma are unreliable

Background-A study was undertaken to investigate the compliance with and ac curacy of peak flow diaries in childhood asthma. Methods-Forty asthmatic children (5-16 years) were asked to perform peak fl ow 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 u naware that the device stored the peak flow values on a microchip. In rando m order, half of the patients were only told that the device allowed for mo re accurate assessment of peak flow while the other half were told that acc urate recording of peak flow was important because the results would be use d in guiding adjustments to treatment. Data in the written diary (reported data) were compared with those from the electronic diary tactual 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 e ntries 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 ran ged from -72 to 34 l/min per patient. Conclusions-Peak how diaries kept by asthmatic children are unreliable. Ele ctronic peak flow meters should be used if peak how monitoring is required in children with asthma.