Supplementary Material for: Inconsistent skin prick tests for allergy to birch homologous trees may result from cross-reacting allergens or technical errors

Introduction: Skin prick tests (SPTs) are the gold standard for diagnosis of allergic rhinitis (AR). A decrease in the number of allergens included in standard SPT panels has recently been debated—particularly regarding the cross-reacting homologous pollen from birch, alder and hazel trees—but has not yet been implemented in clinical guidelines. Methods: A subgroup of patients with AR (n=69) who showed inconsistent SPT results among birch, alder and hazel was investigated in detail. Beyond SPT, patient workup included assessment of clinical relevance and various serological parameters (total IgE, and specific IgE to birch, alder and hazel, and to Bet v 1, Bet v 2 and Bet v 4). Results: More than half the study group had negative SPT results for birch but positive results for alder and/or hazel, and 87% of the study group was polysensitized, showing at least one more positive SPT result for other plants. Whereas 30.4% of patients showed serological sensitization to birch pollen extract, only 18.8% displayed positive specific IgE to Bet v 1. Clinical assessment revealed that most patients with AR were polysensitized and had perennial symptoms or symptoms also occurring during times other than tree flowering times. If the SPT panel is limited to testing birch only, 52.2% of patients in this subgroup would have been overlooked. Discussion/Conclusion: Inconsistent SPT results in the birch homologous group may result from cross-reacting allergens or technical errors. If patients report convincing clinical symptoms despite negative results from a reduced SPT panel or inconsistent results for homologous allergens, SPT should be repeated, and molecular markers should be added to achieve a correct diagnosis.