Relation of changes in PEF and FEV1 in exercise challenge in children

Abstract

Decrease in forced expiratory volume in one second (FEV₁) of 10% or 15% in exercise challenge test is considered diagnostic for asthma, but a decrease of 15% in peak expiratory flow (PEF) is recommended as an alternative. Our aim was to assess the accuracy of different PEF cut-off points in comparison to FEV₁.

We retrospectively studied 326 free running exercise challenge tests with spirometry in children 6−16 years old. FEV₁ and PEF were measured before and 2, 5, 10 and 15 min after exercise. Receiver operating characteristics (ROC) analysis, sensitivity, specificity, positive and negative predictive values (PPV and NPV) and ϰ-coefficient were used to analyse how decrease in PEF predicts decrease of 10% or 15% in FEV₁.

In the ROC analysis, areas under the curve were 0.851 (p < 0.001) and 0.921 (p < 0.001) for PEF decrease to predict a 10% and 15% decrease in FEV₁, respectively. The agreement between changes in PEF and FEV₁ varied from slight to substantial (ϰ values of 0.199–0.680) depending on the cut-points. Lower cut-off for decrease in PEF had higher sensitivity and NPV, while higher cut-off values had better specificity and PPV. Decrease of 20% and 25% in PEF seemed to be the best cut-offs for detecting 10% and 15% decrease in FEV₁, respectively. Still, a fifth of the positive findings based on PEF were false.

Change in PEF is not a precise predictor of change in FEV₁ in exercise test. The currently recommended cut-point of 15% decrease in PEF seems to be too low and leads to high false positive rate.