Use of Skin Prick Test, Specific IgE to Shrimp and Rpen a1 to Determine Clinical Reaction to Shrimp in Area with High Prevalence of House Dust Mite Sensitization

Background: Shrimp is a widely consumed shellfish and the most common cause of anaphylaxis in Southeast Asia. Diagnosis of shrimp allergy using skin prick test(SPT) or specific IgE(sIgE) may be interfered by sensitization to house dust mite(HDM) which is also prevalent in the area. Sensitization to both allergens can occur due to cross reaction by tropomyosin.

Objective: In this study we sought to evaluate the roles of SPT to shrimp, sIgE to shrimp or component resolved diagnostic in the diagnosis of shrimp allergy in area with high prevalence of HDM sensitization.

 Methods: Subjects with sensitization to shrimp and Dermatophagoides pteronyssinus (Derp) determined by SPT were enrolled from the allergy clinic. Shrimp allergy was diagnosed by oral food challenge test or convincing history of repeated allergic symptoms after shrimp ingestion or history of shrimp induced anaphylaxis. Mean wheal size of SPT to shrimp extract, cooked Pacific white shrimp, sIgE to Der p, shrimp and rPen a1 were determined.

Results: Fifty-one subjects were enrolled and classified into 2 groups according to shrimp reactions; shrimp allergy (n=22) and shrimp tolerance (n=29). Ages of shrimp allergic subjects ranged from 4 to 66 years, with 45% were male and 55 % were female. One-third of subjects with shrimp allergy had isolated oral itching symptoms while half of subjects had anaphylaxis. Median SPT wheal size to shrimp extract and fresh shrimp were significantly higher in shrimp allergic subjects compared to shrimp tolerance; 6.25 vs 4.25 mm, p=0.022 and 7 vs 4.5 mm, p=0.003 accordingly. SPT to shrimp extract >3.5 mm or positive shrimp sIgE(>0.35 kUA/) provided 90% sensitivity and negative predictive value (NPV) of 0.86. SPT to fresh shrimp provided better sensitivity and NPV (95% and 0.90) than shrimp extract. Using the cut of value of 0.35, sIgE to rPen a1 was found to have low sensitivity (45%) but high specificity (85%) and positive predictive value of 0.71 in identifying patients with shrimp allergy. Size of SPT, levels of shrimp sIgE and sIgE to rPena1 were not significantly difference between anaphylactic and non-anaphylactic subjects. 

 Conclusions: In subjects who demonstrated sensitization to both shrimp and HDM, sIgE to rPen a1 can be helpful in predicting clinical reaction while SPT and sIgE to shrimp are good screening tests. SPT to fresh shrimp had higher sensitivity and NPV than shrimp extract. SIgE to rPen a1 cannot be used to predict severity in our shrimp allergic population.