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 fluoroimmunoassay (Pharmacia & Upjohn, Uppsala, Sweden), in 30 consecutive patients who presented at the emergency room with a clinical allergic reaction of less than 6-h duration to assess the value of this method in the diagnosis of anaphylaxis. Anaphylaxis was established by clinical criteria and by immunoallergic study. Baseline tryptase levels were determined 1 month later in 21 patients. The receiver operating curve (ROC) was used to establish the best 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 mostly 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 manufacturers showed 35.29% sensitivity and 92.31% specificity. The reaction-tryptase/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 fluoroimmunoassay identify anaphylaxis in patients with symptoms of less than 6-h duration. The usefulness of this determination is higher if baseline tryptase levels are available.