The major allergen content of allergenic preparations reflect their biological activity.

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.