Usefulness of UniCAP-tryptase fluoroimmunoassay in the diagnosis of anaphylaxis

Background: Serum tryptase level measured by RIA is the main in vitro tool to confirm the diagnosis of anaphylaxis. Methods: Serum tryptase levels were determined by UniCAP-Tryptase fluoroimm unoassay (Pharmacia & Upjohn, Uppsala, Sweden), in 30 consecutive patients who presented at the emergency room with a clinical allergic reaction of le ss than 6-h duration to assess the value of this method in the diagnosis of anaphylaxis. Anaphylaxis was established by clinical criteria and by immun oallergic study. Baseline tryptase levels were determined 1 month later in 21 patients. The receiver operating curve (ROC) was used to establish the b est cutoff point of tryptase levels to confirm the diagnosis of anaphylaxis . Results: Seventeen patients were diagnosed with anaphylaxis. In this group, tryptase levels were higher than in the nonanaphylaxis group, composed mos tly of patients with urticaria or angioedema (P<0.001). ROC established the best cutoff of tryptase levels at 8.23 ng/ml with a 94.12% sensitivity and 92.31% specificity, whereas the 13.5 ng/ml cutoff recommended by the manuf acturers showed 35.29% sensitivity and 92.31% specificity. The reaction-try ptase/baseline-tryptase ratio was 2.85 in the anaphylaxis group and 1.29 in the nonanaphylaxis group. Conclusions: Serum tryptase levels of >8.23 ng/ml by UniCAP-Tryptase fluoro immunoassay identify anaphylaxis in patients with symptoms of less than 6-h duration. The usefulness of this determination is higher if baseline trypt ase levels are available.