Insect allergy. Predictive value of diagnostic tests: a three-year follow-up study.

One hundred and six adults with various reactions to yellow jacket (YJ), honey bee (HB) or unidentified insects (UI) were tested for allergy to insect venoms. For various reasons none received immunotherapy. Individuals completed questionnaires annually for three consecutive years and described sting reactions within the previous season. Ninety subjects completed all the questionnaires and 77 of these were re-tested at the end of the period. Nine out of 25 patients reacted with a systemic reaction when re-stung. High IgE and low IgG venom-specific antibody levels indicated an unfavourable prognosis, since eight of 11 individuals who initially presented venom-specific IgE greater than RAST class 2 and venom-specific IgG below detection limit had systemic reactions at re-sting. No such reactions occurred in subjects with no specific IgE and only one out of six with specific IgE as well as IgG reacted systematically. Skin prick tests (SPT) of less than 3mm with YJ venom 1,000 micrograms/ml excluded later systemic symptoms to stings, whereas larger skin reactions gave an equal chance of systemic or local reactions at re-sting. In individuals not stung by UI, YJ and/or HB the decline in venom-specific IgG and IgE was significant, median values ranging from 41% to 75% over the 3-year period. The decline was unaffected by the type of sting reaction prior to the initial test. SPT results did not change significantly. The findings are relevant when testing patients several years after their last insect sting and the results might indicate that the antibody decline is accompanied by a decrease in clinical sensitivity.