BSA Interference in Immunoassays in Individuals with Egg Allergy

Aim: The aim of current study was to determine interference by bovine serum albümine (BSA) as blocking agent in enzyme-linked immunosorbent assay (ELISA) carried out in individuals with egg allergy. Material and Methods: 14 people diagnosed with egg allergy and 7 people without allergy were included. The sample were studied with an indirect ELISA method for egg-white IgG antibody developed in our laboratory. Effect BSA on interference was studied by manipulating antigene coating (none vs. egg white extract), blocking (1% BSA vs. Tween 80), and sample diluent (PBS vs. PBS + 0.5% BSA). Results: In wells that were blocked with 1% BSA without being coated with antigen, positive samples cross-reacted with BSA to give an optical density (OD) of 0.99 ± 0.16, while negative samples gave an OD of 0.08±0.01 (p<0.05). However, when the same samples were diluted with 0.5% BSA, the OD of positive samples decreased (from 0.99±0.16 to 0.08±0.01), and the statistical difference with negative samples disappeared. It was observed that tween, which was used as a blocking and diluting agent, did not cross-react with the samples. Positive samples gave an OD of 0.66±0.07 in antigen (egg white extract) coated and tween-blocked wells, and 1.01±0.11 OD in BSA blocking (p<0.05). When the samples were diluted with 0.5% BSA, positive samples gave 0.18±0.01 OD on the antigen coated plate, while negative samples gave 0.12±0.04 OD (p<0.05). Conclusion: Ovalbumin, which is found in high levels in eggs, has a similar molecular structure to BSA, and some antibodies produced against ovalbumin in people with egg allergy may also cross-react against BSA. Therefore, it was concluded that the use of BSA in both dilution and blocking solution should be avoided if the samples of individuals with egg sensitivity are to be analyzed by ELISA method. It has been observed that Tween can be easily applied as an alternative blocking agent in allergy ELISA tests.