2010 Oct - The Prevalence of Positive Skin Prick Test to Common Aeroallergens in Allergic Asthma Patients in a Regional Hospital
Dr Yeung Koon-sing, Tuen Mun Hospital
Atopic asthma is a common disease affecting many people. Avoidance therapy to the aeroallergens is a cost-effective and safe measure to help atopic asthma patients. Skin prick test (SPT) is a well-established method to identify the responsible allergens. The SPT positive subjects might potentially be benefited from immunotherapy and/or the anti-immunoglobulin E (anti-IgE) therapy if clinically indicated. However, local data on the prevalence of identifiable aetiological aeroallergens by skin prick test among adult patients with atopic asthma is lacking.
To study the prevalence of SPT-positivity of common aeroallergens in atopic asthma patients and to compare their clinical characteristics with the SPT-negative individuals.
This is a prospective observational study. Adult patients with atopic asthma and allergic rhinitis attending a specialist respirology clinic from June 2009 to January 2010 undergone SPT on common aeroallergens (including house dust mite, tree/grass pollen, moulds, cat, dog and cockroach) and who consented to participate in the study were recruited. The SPT reagents were produced by ALK-abello (Denmark). SPT provides information about the presence of specific immunoglobulin-E to protein and peptide antigens. Small amount of allergens is introduced into the epidermis and superficial dermis by sterile lancet, which interact with specific IgE bound to the cutaneous mast cells. Histamine and other mediators are released, leading to visible induction of “wheal-and-flare”. That would be regarded positive if the mean diameter is at least 3mm larger than the negative control. Demographic data, serum total IgE levels, current management grading of asthma, knowledge of avoidance therapy and self-predictive SPT result, etc. are compared between the SPT positive and negative groups.
One hundred and four patients were recruited during the study period. Ninety seven patients (93.3%) patients were tested positive to at least one of the eight common aeroallergens by SPT, with dust mite being the commonest culprit. The SPT-positive patients showed a trend to be more likely having positive family history of atopy and higher serum total immunoglobulin E (IgE) levels comparing to their SPT-negative counterparts. Less than 23% of the patients had ever heard of avoidance therapy before this study.
Allergies to aeroallergens have been found to be common in patients with atopic asthma. Skin prick test is useful to identify these patients, who may potentially be benefited from immunotherapy and anti-IgE therapy. Education on allergen avoidance has been insufficiently provided and should be promoted with additional efforts.