The diagnosis of severe hazelnut allergy relies on skin prick tests (SPTs), specific IgE assay and oral challenge. However, SPTs with crude hazelnut or commercial extracts may produce false positives in people with benign, pollen-driven allergy. We therefore studied the predictive value of a SPT based on grilled hazelnut, containing only thermostable allergens.
73 children sensitized to raw hazelnut were enrolled. They underwent a SPT with grilled hazelnut, and a double-blind, placebo-controlled food challenge (DBPCFC) with raw hazelnut. 36 of the children were clinically allergic to hazelnut (with objective symptoms after exposure to less than 20 g of hazelnut), and 37 served as controls (sensitized to hazelnut but negative DBPCFC).
In the DBPCFC, the reaction threshold ranged from 1.4 mg to 20 g, with a mean of 2.2±3.9 g. In the SPT with raw hazelnut, the mean wheal diameter was 12.7±5.6 mm in allergic patients, and 4.9±3.4 in controls (p<0.0001). In the SPT with grilled hazelnut, the wheal diameter was 9.3±5.4mm for allergic patients and 1.5±2.8 for controls (p<0.0001). Using a cut-off wheal diameter of 4.0 mm, a ROC curve showed that the SPT with grilled hazelnut had a sensibility of 81%, a specificity of 84%, a PPV of 83%, and a NPV of 82%. Sensitization to grilled hazelnut was a good predictor of the severity of the reaction (p<0.0002), whereas sensitization to raw hazelnut was not (p<0.11).
A skin prick test with grilled hazelnut is a valuable marker that can help the clinician to distinguish between severe hazelnut allergy and benign hazelnut sensitization.