Introduction and Objectives We wished to examine therelationships between inflammation (FE_NO),methacholine challenge (AHR) and airway calibre (FEV1%) in a group of mild-to-moderate asthmatics.

Methods We searched our patient database forthose individuals with a known diagnosis of asthma who had a methacholine PC₂₀≤ 8 mg/ml. Data regarding FEV1%, FE_NO, skinprick and methacholinePC₂₀ were collected and divided into groups based upon AHR: severe (<0.5 mg/ml), moderate (>0.5–2 mg/ml) and mild (>2–8 mg/ml); and FE_NO: low (<25 ppb), medium (25–50 ppb) and high (>50 ppb).

Results We identified 208 who had a known diagnosis of asthma, a methacholinePC₂₀ ≤8 mg/ml, as well as FE_NO and skin prick testing. Mean age (SEM) was 41.1 (1). There was an 8.5% difference in FEV1% between groups A and C, (95% CI (2.6% to 14.4%) p=0.002) and a 29% difference for FE_NO between groups A and C, (95%CI (2% to 48%) p=0.034). There was a 1.29 doubling dilution difference in methacholinePC₂₀ (95%CI (0.26 to 2.33) p= 0.009) between groups D and F. There was no significant difference between FEV1% when grouped by FE_NO (See Abstract P25 Table 1). Applying multiple stepwise linear regression showed that FE_NO and FEV1% were both significant predictors of methacholine PC20 (p= 0.002, p<0.001). Only methacholine PC₂₀ was a significant predictor of FE_NO (p=0.002).

Conclusion Our study has highlighted the disconnect between airway inflammation and airway calibre, whilst showing a significant relationship between AHR versus airway calibre and inflammation. Thus, whilst relationships exist between these independent outcomes, the lack of complete concordance highlights the important role that each contributes to the assessment of the asthmatic individual.