The diagnostic and screening capacities of peak expiratory flow measurements in the assessment of airway obstruction and bronchodilator response in children with asthma.

Although the measurement of peak expiratory flow (PEF) is frequently used in general practice as a surrogate for forced expiratory volume in one second (FEV1) in the assessment of airway obstruction and bronchodilator response (BDR), its use has never been validated in children with asthma. Spirometry and PEF measurements (mini-Wright peak flow meter) were performed in 271 children with asthma who attended the hospital for a routine pulmonary evaluation. Airway obstruction was defined as FEV1 as a percentage of predicted (FEV1% pred) < 80%; a positive BDR was defined as an increase in FEV1% pred > or 9% after inhaling 800 micrograms salbutamol. The Spearman correlation coefficient between the percent-predicted values of PEF (PEF% pred) and FEV1% pred was 0.36, Commonly used cut off values for airway obstruction of PEF% pred < 75% and PEF% pred < 80% had a high specificity (95%, 91%) and NPV (95%, 95%), but a moderate sensitivity (54%, 57%) and PPV (54%, 41%). After administration of the bronchodilator, the Spearman correlation coefficient between the different expressions of delta PEF and delta FEV1% pred ranged between 0.52 and 0.54. Commonly used cut off values for BDR of delta PEF% init (increase in PEF as percentage of initial value) > or = 20% and delta PEF% init > or = 25% had a high specificity (96%, 96%), a reasonable NPV (74%, 69%) and PPV (74%, 85%), but a moderate sensitivity (51%, 53%). In conclusion, PEF testing has the properties to be a good screening test to exclude airway obstruction and BDR (high specificity and NPV), but is of less clinical value as a diagnostic test (moderate sensitivity and PPV).