The content of major allergens in biologically standardized allergenic preparations of birch, mite (Der p), cat, Alternaria (Alt a) and ragweed (Amb e) was determined. It was found fairly constant between species, i.e. varied within a factor of 2, with the exception of Alt a 1 in Alternaria alternata extract. This variation is allowed by authorities between different batches prepared from the same species of allergen. The method for biological standardization (BS) prescribed in the Nordic Guidelines has, for common inhalant allergens, been shown to give reproducible results between regions of Europe. However, it is difficult to define patients suitable for BS of most food allergens as well as less common inhalant allergens. Therefore we propose that, in the future, BS is replaced by determination of well-established major allergens and that 1 ng of major allergen is given the value of 1 Biological Unit.
Clinicians have had difficulties in understanding differences and similarities between units used by manufacturers for labelling of allergenic extracts. Biological standardization is time-consuming and expensive. Probably therefore, and to avoid comparison with extracts prepared by other manufacturers, most manufacturers have used their own units and few of them have used the biological units as defined by the Nordic Guidelines or FDA. Determination of the amount of major allergen by ELISA is simple and cheap. However, the biological relevance of major allergen content has not been established. Our results clearly indicate the possibility of replacing biological units by major allergen content, provided the composition of allergens is adequate. The major allergen content can easily be declared by all manufacturers. In the future, manufacturers should be forced to declare the major allergen content, thus making it easier for clinicians to compare extracts from different suppliers.