The usefulness of tryptase formula for the diagnosis of shrimp-induced anaphylaxis
Monday, March 5, 2018
South Hall A2 (Convention Center)
Thunyatorn Phisitbuntoon, MD, Patcharaporn Wongkaewpothong, Punchama Pacharn, MD, Nualanong Visitsunthorn, MD, Pakit Vichyanond, MD FAAAAI, Orathai Jirapongsananuruk, MD
RATIONALE: Serial measurements of serum tryptase compared to baseline levels were shown to be better predictors of anaphylaxis than a single peak serum tryptase. The objective of our study was to validate the performance of the suggested formula of peak serum tryptase level more than 2 µg/L+1.2 x (baseline tryptase) for the diagnosis of shrimp-induced anaphylaxis.
METHODS: Data of serum tryptase level at baseline and 1 hour after symptom occurred were obtained from 39 patients with history of shrimp allergy who underwent open shrimp challenges.
RESULTS: The challenges revealed 12 patients with anaphylaxis, 20 with mild reaction and 7 without reaction. The ROC curve showed the best cutoff point for serum tryptase ratio was ≥1.5 and for delta tryptase was ≥0.8 µg/L with 91.7% sensitivity, 96.3% specificity, 91.7% PPV, 96.3% NPV, 23 positive likelihood ratio (LR) and 0.08 negative LR and 83.3% sensitivity, 92.6% specificity, 83.3% PPV, 92.6% NPV, 11.86 positive LR and 0.18 negative LR, respectively. The suggested formula showed 33.3% sensitivity, 100% specificity, 100% PPV, 77.1% NPV, infinity positive LR and 0.67 negative LR. The performances of tryptase ratio ≥1.5 and delta tryptase ≥0.8 µg/L were not significantly different. However, both value performed significantly better than the suggested formula (P=0.008). Moreover, when compared with single peak serum tryptase ≥11.4 µg/L, the formula did not show better performance (P=1).
CONCLUSIONS: Peak serum tryptase level more than 2 µg/L+1.2 x (baseline tryptase) may not be a good predictor of shrimp-induced anaphylaxis.