Screening for Compositae sensitization with pure allergens: implications of molecular structure, strength of reaction, and time of testing

Background. The sesquiterpene lactone (SL) mix is the only commercial Compositae allergy screening agent that consists of pure allergens; its detection rate is lower than that of Compositae plant extracts. Objective(s). To report a 15‐year experience with routine screening with SL mix and another allergen, parthenolide, the optimal reading times when testing with SL mix constituents, and the advantages and drawbacks of using pure allergens. Materials and methods. The SL mix 0.1% and parthenolide 0.1% petrolatum were included in the baseline series. Results. Of individuals undergoing routine testing, 157/7163 (2.19%) tested positive to SL mix, 161/7162 (2.25%) to parthenolide, and 141 to both in the 15‐year period. The overall detection rate between the two was 177 persons, and 10% would have been missed without parthenolide testing. Two cases of possible active sensitization to parthenolide were recorded. Costunolide elicited positive reactions most frequently, followed by dehydrocostus lactone, and alantolactone. An important observation was that the prevalence of positive reactions to SL mix constituents was lower if they were applied 3–5 days after application of SL mix in those with 1+ or 2+ reactions. Conclusions. The benefit of detecting 10% more Compositae‐sensitive patients with parthenolide in the baseline series must be weighed against a small risk of active sensitization, which may be reduced by lowering the test concentration.