Patients with a history of shrimp
allergy and positive skin prick tests (SPT) to commercial shrimp extract were recruited for shrimp challenges. Serum total
tryptase was obtained at baseline and 60 min (peak) after the onset of symptoms.
RESULTS: Thirty-nine patients were challenged. There were 12 patients with
anaphylaxis, 20 with mild reactions and 7 without symptoms (control group). Characteristic features and baseline
tryptase were not different among the 3 groups. The peak
tryptase levels were higher than the baseline in
anaphylaxis and mild reaction groups (P<0.05). The
delta-tryptase (peak minus baseline) and the
tryptase ratio (peak divided by baseline) in the
anaphylaxis group were higher than the mild reaction and control groups (P<0.01). The optimum cut-off for peak
tryptase to confirm
anaphylaxis was 2.99 µg/L with 50% sensitivity, 85% specificity, 3.33 positive likelihood ratio (LR) and 0.59 negative LR. The manufacturer's cut-off for peak
tryptase was >11.4 µg/L with 17% sensitivity, 100% specificity, infinity positive LR and 0.83 negative LR. The best cut-off for
delta-tryptase was ≥0.8 µg/L with 83% sensitivity, 93% specificity, 11.86 positive LR and 0.18 negative LR. The best cut-off for
tryptase ratio was ≥1.5 with 92% sensitivity, 96% specificity, 23 positive LR and 0.08 negative LR.
CONCLUSIONS: The peak
tryptase level should be compared with the baseline value to confirm
anaphylaxis. The
tryptase ratio provide the best sensitivity, specificity, positive and negative LR than a single peak serum
tryptase for the confirmation of shrimp-induced
anaphylaxis.