Key points
Diagnosis (see Table 5)
Diagnosis relies strongly on medical history. Clinical presentation of skin lesions is, in itself, rarely diagnostic of a particular insect. Flea and bedbug bites frequently display a characteristic pattern known as “breakfast, lunch, and dinner”.128
Commercial extracts for skin testing and in vitro IgE determination are available only for a very limited number of species. They are, throughout, whole-body extracts with low sensitivity due to small amounts of relevant saliva allergens.91,114,129They also have low specificity since they contain inhalant allergens unrelated to insect bite hypersensitivity (e.g. tropomyosin).91,129 Irrelevant IgE-binding may also occur through CCDs.130 Several saliva allergens have been expressed as recombinant proteins, yet none of them has become commercially available for routine diagnosis.
The expected benefits of improved IgE diagnostics need to be clarified. IgE testing may be decisive in hypersensitivity to insects rarely causing sensitization but less so in, for example, mosquito allergy where up to 80% of the general population show type 1 sensitization.85 IgE levels in “allergic” subjects and those with “normal” skin reactions substantially overlap making detection of discriminative cut-off levels difficult.99,131 Significant morbidity in insect bite hypersensitivity is linked with delayed cell-mediated large local reactions where IgE-directed diagnostics may have limited value. Another diagnostic problem is the large number and geographic variability of relevant insect species and the uncertain cross-reactivity between them.