Diagnostic Accuracy of Specific IgE Against Wheat and Rye in Flour-Induced Occupational Asthma

BACKGROUND Assessment of IgE-mediated sensitization to flour allergens is widely used to investigate flour-induced occupational asthma. The diagnostic efficiency of detecting specific IgE antibodies (sIgE) against wheat and rye flour, however, has not been thoroughly compared to other diagnostic procedures. OBJECTIVE We sought to evaluate the diagnostic accuracy of sIgE against wheat and rye compared to specific inhalation challenge (SIC) with flour as the reference standard. METHODS This retrospective multicenter study included 264 subjects who completed a SIC with flour in eight tertiary centers, of whom 205 subjects showed a positive SIC result. RESULTS Compared with SIC, sIgE levels ≥0.35 kUA/L against wheat and rye provided similar sensitivities (84%-85%, respectively), specificities (71%-78%), positive predictive values (91%-93%), and negative predictive value (56%-61%). Increasing the threshold sIgE value to 5.10 kUA/L for wheat and to 6.20 kUA/L for rye provided a specificity ≥95% and further enhanced the positive predictive value to 98%. Among subjects with a positive SIC, those who failed to demonstrate sIgE against wheat and rye (n=26) had significantly lower total serum IgE level and blood and sputum eosinophil counts, and a lesser increase in post-challenge fractional exhaled nitric oxide as compared to the subjects with detectable sIgE. CONCLUSION High levels of sIgE against wheat and/or rye flour strongly support a diagnosis of flour-induced occupational asthma without the need for performing a SIC. The absence of detectable sIgE against wheat and rye in subjects with a positive SIC seems to be associated with lower levels of TH2 biomarkers.