Introduction: Assessment of immunodeficiency in patients with BE includes assessment of the ability to make co-ordinated B and T cell responses to polysaccharide antigens, assessed by testing PNE and/or HiB vaccination response. We evaluated the frequency of testing for antibody responses and the characteristics of patients with abnormal responses in EMBARC.

Methods: The EMBARC registry enrolled patients from 28 European Countries with CT confirmed BE, followed-up for up to 5 years.

Results: 3904 patients (23.0%) had functional antibody testing performed. Testing was most commonly performed in the UK (37.6%) and Northern and Western Europe (15%) and rarely performed in Southern Europe (7.2%) and Central and Eastern Europe (0.8%). We found 661 patients (16.9% of those tested) with an abnormal functional antibody response. These patients had similar characteristics to those with normal responses in terms of age, sex and disease severity but they were more likely to experience severe exacerbations (RR 1.26, p=0.024) at follow-up. After adjustment for age, sex, Pseudomonas infection, lung function and region, abnormal functional antibody responses remained associated with severe exacerbations (RR 1.39, p=0.002).

No association was found with mild exacerbations (RR 1.10 95%CI 0.96-1.25p-=0.19) or survival (HR 0.86 95%CI 0.59-1.25,p=0.42). Only 48 patients had a formal diagnosis of specific polysaccharide antibody deficiency.

Conclusion: Functional antibody testing is infrequently used as part of assessment of BE patients in Europe. Patients with abnormal functional antibody responses are at higher risk of severe exacerbations.