BACKGROUND: Wheat is an important food allergen associated with severe allergic reactions, including wheat-dependent exercise-induced anaphylaxis (WDEIA) and wheat-induced anaphylaxis (WIA). To diagnose WDEIA, an exercise challenge test following wheat ingestion is performed, which is time-consuming and unsafe. The compound ω-5 gliadin has been identified as a major allergen for WDEIA and WIA. We evaluated the diagnostic value of serum immunoglobulin E (IgE) ratios of ω-5 gliadin to wheat in adult patients with WDEIA or WIA. METHODS: In total, 27 patients were enrolled and classified into 2 groups according to the severity of their allergic reactions to wheat. Serum IgE, specific to wheat and ω-5 gliadin, was measured using the ImmunoCAP system. To evaluate the diagnostic value, receiver operator characteristic curves were produced. RESULTS: Group 1 included 17 patients with a history of anaphylaxis and group 2 included 10 patients having urticaria or atopic dermatitis. Serum IgE specific to wheat was increased in 47% of group 1 and 100% of group 2. However, all patients in group 1 had high serum IgE specific to ω-5 gliadin, whereas only 20% of group 2 showed increased levels. To identify a better diagnostic value, the log-transformed IgE ratio of ω-5 gliadin to wheat was calculated, with the cutoff value at 0.3. Based on these criteria, we found 100% sensitivity and specificity. CONCLUSIONS: This study confirms that the serum IgE ratio of ω-5 gliadin to wheat may be a useful marker for the diagnosis of WDEIA and WIA.