Relationship between exhaled nitric oxide and IgE sensitisation in patients with asthma: influence of steroid treatment

Abstract

INTRODUCTION: The influence of the degree of immunoglobulin E (IgE) sensitisation on the fraction of expired nitric oxide (FE(NO)) in asthma patients being treated with inhaled corticosteroids (ICS) is not well known. OBJECTIVES: To investigate the relationship between IgE sensitisation and FE(NO), and the effect of a step-up in ICS treatment on this relationship, in patients with allergic asthma. METHODS: A primary health care centre recruited 20 non-smoking patients with perennial allergic asthma (18 years-50 years, six male) outside the pollen season. At every visit (0, 2, 4, 8 weeks), FE(NO) was measured and an exposure questionnaire was completed. ICS dose was adjusted according to FE(NO) (>or=22 ppb prescribed increase in ICS). Quantitative analyses of serum IgE (eight common aeroallergens) confirmed allergy. RESULTS: At baseline, FE(NO) and the sum of IgE antibody titres for perennial allergens correlated significantly (r = 0.47, P = 0.04). After a step-up in ICS treatment, this correlation had disappeared. Nine patients had persistently elevated FE(NO) at last visit (mean 35 ppb vs 16 ppb). This group was more frequently exposed to relevant allergens or colds (89% vs 27% of patients, P < 0.05) and had higher IgE antibody titres (perennial allergens) compared with the normalised group (mean 28.9 kU/L vs 10.7 kU/L, P < 0.05). CONCLUSION: Serum IgE against perennial allergens and FE(NO) correlate in patients with allergic asthma. However, this relationship disappears after a high-dose ICS regimen, suggesting that FE(NO) relates to bronchial inflammation and not IgE levels per se. High degree of IgE sensitisation together with allergen exposure may lead to ICS-resistant airways inflammation.