Using % predicted change during bronchial challenge testing to remove bias

The methacholine challenge assesses bronchial hyper-reactivity, reporting the provocative dose causing a 20% fall in FEV₁ (PD₂₀). Patients with low baseline values require a smaller volume fall compared to those with higher baseline values, introducing bias. Change in % predicted has been advocated for reversibility testing to remove this bias, but this has not been employed in bronchial challenge testing. <bold>Aim:</bold> To evaluate % predicted decrease during bronchial challenge. Data from 15 asthma patients was assessed. Methacholine challenge was performed as per ERS 2017 guidelines, utilising a 20 second protocol with a jet nebuliser (AeroEclipse BAN II). Change in % predicted was calculated at each dose as ((FEV_1meth-FEV_1pre)*100)/FEV_1pred. PD values based on fall in % predicted were compared to PD₂₀ using Wilcoxon test, with p < 0.05 considered significant. The fall in % predicted that equated to a 20% fall from baseline (figure 1) ranged from 14.7% to 22.2%. A PD value using a 15% fall in predicted was significantly lower than PD₂₀ (median: 14µg vs 21µg, p = 0.0002), and would have resulted in 3 patients requiring one less dose of methacholine. Using % predicted value may reduce bias in bronchial challenge testing, whilst maintaining discriminatory capability for hyper-reactivity. <fig><object-id>erj;64/suppl_68/OA4588/F1</object-id><object-id>F1</object-id><object-id>F1</object-id><graphic></graphic></fig> Figure 1. Grey bars – fall in % predicted that equated to a 20% fall from baseline FEV₁. Grey lines - actual fall in % predicted at consecutive methacholine doses.