Total IgE in urban Black South African teenagers: the influence of atopy and helminth infection.

Total IgE levels are usually elevated in allergic diseases, being highest in atopic eczema, followed by atopic asthma and allergic rhinitis. Genetic factors are believed to play a role in total IgE levels, with higher levels seen in Black African subjects. Total IgE is also raised in parasite infection. Thus, the higher total IgE levels in Black Africans could be because of environmental rather than genetic factors. Few studies have investigated the usefulness of total IgE levels in the evaluation of atopy in Black Africans. The objective of this study was to determine the total IgE levels in unselected urban Black African high school children and to correlate this with atopy and ascaris sensitization. Atopic status was assessed by means of specific allergen sensitization (skin prick tests to eight inhalant and four food allergens), self-reported asthma and bronchial hyper-responsiveness measured by methacholine challenge. Ascaris sensitization was assessed by means of ascaris IgE measured by CAP-RAST. Total IgE levels were markedly skewed toward the left and were not distributed in a Gaussian or a log-normal distribution. Skin prick tests were positive for aeroallergens in 32.3% of subjects. Thirty four percent had elevated ascaris IgE. Total IgE was higher in atopic vs. non-atopic subjects and correlated with the number of positive skin prick tests, self-reported asthma and bronchial hyper-responsiveness. Subjects without allergy (or) atopy had a median total IgE of 80-90 kU/I. In addition total IgE correlated with ascaris IgE. Subjects with no ascaris sensitization had median total IgE of 77.1 kU/l. Subjects with neither atopy/asthma nor ascaris sensitisation had a median total IgE of 69.9 kU/I, similar to the levels seen in people of other genetic origins. This study suggests that helminthic infection rather than genetic differences, may be the major determining factor of IgE levels in certain populations.