Anisakis/Ascaris IgE ratio improves specificity for the diagnosis of Anisakis simplex sensitization in travellers and immigrants

Anisakis simplex is a fish parasite responsible for human infection and is able to induce IgE-mediated reactions with several clinical manifestations. Laboratory diagnosis of Anisakis allergy is based on the detection of specific IgE using parasite whole antigen. Unfortunately, these diagnostic tools detect cross-reactivities with other nematodes and micro-organisms leading to low specificity of the diagnostic tests. The aim of this retrospective study was to assess the diagnostic value of specific IgE to Anisakis for diagnosis of A. simplex-sensitization in native Spanish residents (IMM, n = 766) and subjects coming from tropical and sub-tropical geographic areas (TRO, n = 233). Since Ascaris is the human parasite most closely related to Anisakis, specific IgE to Ascaris was also determined to assess Anisakis cross-reaction with other nematodes and the diagnostic value of Anisakis/Ascaris IgE ratio for Anisakis allergy was examined. IMM and TRO groups showed similar specific IgE to Anisakis levels, while TRO had higher levels of specific IgE to Ascaris than IMM group (p = 0.001). ROC curve analysis determined that an Anisakis specific IgE threshold of 0.71 kU/L yielded 93% and 82% specificities in IMM and TRO groups, respectively. A cut-off value ≥4.4 for Anisakis/Ascaris IgE ratio increased specificity to 95% for samples having IgE to Ascaris ≥0.35. In conclusion, the ratio of specific IgE to Anisakis and Ascaris improved remarkably the specificity and this parameter easily obtained from the commercially available system could be useful in the diagnosis of hypersensitivity to A. simplex.