# The Advantages of FEV1 Percent Predicted Change During Bronchial Challenge Testing

## TL;DR

This study suggests using a 15% predicted change in FEV1 during bronchial challenge tests instead of a 20% baseline change to better assess airway hyperresponsiveness.

## Contribution

The study introduces a new PD criteria based on 15% predicted FEV1 change, which is less influenced by baseline airflow obstruction.

## Key findings

- PD15% showed significant agreement with PD20 (r = 0.95, p < 0.0001) and higher reliability (ICC = 0.97).
- PD15% required less methacholine and resulted in smaller FEV1 decreases compared to PD20.
- PD15% was not influenced by baseline FEV1, unlike PD20.

## Abstract

The methacholine challenge requires a 20% fall in forced expiratory volume in one second (FEV1). The fall is measured as litre (L) change from the pre-challenge (baseline) value. A higher baseline FEV1 requires a greater volume change to reach a 20% fall. The aim of this study was to evaluate change using percent predicted, which may remove dependence on the baseline value.

Challenge data from a cohort of 114 asthma patients was re-analysed. The dose causing an 20% fall from baseline (PD20) was compared to a 15% fall in predicted value (PD15%) for the classification of bronchial hyperresponsiveness.

There was significant agreement between PD20 and PD15% (r = 0.95, p < 0.0001), with an ICC of 0.97. PD20 was significantly higher than PD15% (0.0055 mg, p < 0.0001). Greater decreases in FEV1 were observed with PD20 versus PD15% (21.4% pred vs 19.1% pred respectively, p = 0.0004), with 29% of patients requiring at least one additional dose of methacholine to achieve PD20 compared to PD15%. A higher baseline FEV1 resulted in higher PD20 values, whereas no relationship was found for PD15%. Variability in FEV1 between repeated visits (n = 15) was associated with the change in PD20, but not the change in PD15%.

We suggest a PD criteria based on 15% predicted change should be used for bronchial challenge testing. This method is less influenced by baseline airflow obstruction, and is a more efficient and safer way of measuring airway hyperresponsiveness.

The online version contains supplementary material available at 10.1007/s00408-025-00823-5.