Skin testing technique and precision in stinging insect allergy

Aim. We report on quantitative analysis of skin tests in patients undergoing Hymenoptera venom immunotherapy. The need for accuracy, coupled with a sound manual technique, in performing this procedure is emphasized. Involuntary errors may occur and pose serious problems with interpretation of results. A revealing example is reported and the strategy devised to analyse the flaws and overcome the resulting problems is presented and discussed. Background. Skin testing plays a key role in the diagnosis of most allergic disease and in the assessment of allergen immunotherapy. Particularly, insect sting allergy requires implementation of complex and demanding skin testing protocols and a competent nursing practice. Methods. Sixteen patients were tested before starting the immunotherapy and after three years of treatment. Cutaneous response (expected to decline, following immunotherapy) was assessed as: (i) allergen-elicited wheal areas; (ii) ratios between allergen-elicited wheal areas and homologous histamine (positive controls) wheal areas. Results. By using allergen-elicited areas, the paradoxical result was obtained that skin reactivity had increased instead of decreasing, upon immunotherapy. Histamine response analysis suggested that this paradox might rather be the result of a technical flaw. Analysis of written notes of routine clinical meetings revealed that an important manual flaw had been detected (and corrected) some years earlier, affecting the results of the baseline testing (viz. the allergen was injected deeper in the skill, yielding a weaker response). Skin reactivity evaluation in terms of allergen-histamine ratio confirmed this interpretation, as, when the baseline ratios were compared with the three years immunotherapy ratios, a distinct decline in skin reactivity was detected, as expected. Conclusions. Skin testing in insect sting allergy is a conceptually and manually complex procedure, which should be subjected to systematic quality control assessment, like a laboratory procedure. The personnel involved in the performance of this procedure should receive appropriate and extensive training. Relevance to clinical practice. Diagnosis of allergic diseases and monitoring of immunotherapy largely rely on impeccable skin testing technique.