Secondary soy allergy in children with birch pollen allergy may cause both chronic and acute symptoms.

Background: Secondary soy allergy occurring in tree pollen allergic patients may cause acute symptoms. Methods: We selected children with birch pollen allergy suspected of also being soy allergic (SA). Soy allergy was proven based on one of the following: (i) a clear-cut clinical history; (ii) a positive provocation test; and (iii) elimination and reintroduction of soy. Skin prick tests (SPT) were performed with a commercial soy extract and with soy flour. Specific IgE to Gly m 4, Gly m 5, and Gly m 6 was determined by means of ImmunoCAP and ISAC. Eight soy-tolerant atopic children being CAP rGly m 4-negative served as a control group for skin testing. Results: Of 15 subjects with birch pollen allergy and being suspected of soy allergy, eight of them proved to be SA; 7/15 subjects proved to be soy tolerant (ST). Besides acute symptoms in 8/8 SA subjects, 3/8 subjects also had been suffering from severe chronic complaints because of soy allergy. SPT with commercial soy extract was negative in all SA and ST subjects tested. SPT with soy flour was positive in 8/8 SA and in 5/6 ST subjects, but negative in all 8 controls (p < 0.0001); the median weal diameter was 7.7 mm in SA subjects, compared to 3 mm in ST subjects (p < 0.01). The median IgE level to rGly m 4 using CAP and ISAC was, respectively, 32.4 kU/l and 4.0 ISU in SA subjects, compared to 6.2 kU/l and 0.4 ISU in ST subjects (p < 0.05). Analysis of IgE to nGly m 5 and nGly m 6, using CAP or ISAC, showed no significant differences between SA and ST subjects. Conclusions: Secondary soy allergy may cause severe chronic besides acute symptoms. SPT with soy flour is a sensitive and specific tool in detecting soy sensitization. SPT with soy flour, CAP rGly m 4, and ISAC rGLY m 4 are valuable tools in the diagnosis of birch-pollen-associated secondary soy allergy.