Shrimp is a common cause of food allergy (1, 2). Symptoms can occur in a single organ such as the skin (e.g., urticaria and lip/tongue swelling), respiratory system (e.g., chest tightening and wheezing), gastrointestinal system (e.g., oral allergy syndrome and vomiting), or cardiovascular system (e.g., low blood pressure). In some cases, multiple organ system involvement occurs such as anaphylaxis in which urticaria and angioedema are the most common accompanying symptoms (3, 4). These reactions usually occur within 2 h after ingestion and involve an IgE-mediated mechanism.

Similar to other food allergies, the conventional investigation tools for immediate-type hypersensitivity reactions to shrimp are skin prick test (SPT), serum-specific IgE (sIgE) for food measurement, or both. Oral food challenge (OFC) is the gold standard tool to exclude or confirm a diagnosis but should be performed under specialist supervision because this procedure might induce a severe allergic reaction (5). However, SPT with shrimp commercial extracts and measurements of sIgE to shrimp have shown low specificities of <50% for a shrimp allergy diagnosis (6, 7). Hence, the definite diagnosis for shrimp allergy remains challenging.

An understanding of allergens, including their specific IgE-binding epitopes, and improvements in technology to produce recombinant allergens allow the development of component-resolved diagnosis (CRD). CRD detects IgE antibodies specific to entire allergenic proteins (components), providing a more precise diagnosis than whole extracts (8). CRD testing has demonstrated high specificity for food allergy diagnosis (e.g., cow's milk and egg) (9). However, reports on using CRD in the diagnosis of shrimp allergy are lacking.

Tropomyosin has been identified as the major shrimp allergen in several shrimp species including Penaeus aztecus (Pen a 1), Penaeus indicus (Pen i 1), Penaeus monodon (Pen m 1), Metapenaeus ensis (Met e 1), and Litopenaeus vanamei (Lit v1) (10, 11). Tropomyosin was shown to share immunodominant epitopes among all species of crustaceans (12). In silico analyses of Lit v 1 show numerous high-identity matches with tropomyosins from multiple shrimp and prawn species (13). A commercial test for measurements of serum IgE to recombinant tropomyosin (rPen a 1) is currently available. However, the accuracy remains controversial. Gámez et al. (14) reported a specificity of 77% for sIgE levels to rPen a 1. In contrast, Ayuso et al. (15) reported a specificity of only 45.5%. One significant factor contributing to the variation in shrimp sensitization is house dust mite (HDM) allergy. This is due to the cross-reactivity between tropomyosin in shrimp and house dust mite (16). It is important to note that Thailand is an HDM-endemic area (17). A small study in this population reported that 30% of patients with shrimp allergy had positive sensitization to HDM (18).

We aimed to evaluate the diagnostic accuracy of measuring sIgE antibodies to tropomyosin in the diagnosis of Litopenaeus vanamei shrimp allergy. We also aimed to compare its diagnostic performance with the results of SPT and the levels of serum-specific IgE antibody to shrimp using commercial testing and recombinant Litopenaeus vanamei IgE testing.

The diagnosis of shrimp allergy remains challenging despite its high prevalence. A key difficulty lies in the complex and species-specific variability of the major allergen, tropomyosin, which contributes to heterogeneity in IgE immune responses. Currently available diagnostic tools, including commercial skin prick testing (SPT) and serum shrimp-specific IgE (sIgE) assays (f24; ImmunoCAP), rely on crude shrimp extracts. The commercial shrimp extract used for SPT (ALK-Abello) is prepared from Litopenaeus setiferus, a prawn commonly found along the Atlantic coast. Meanwhile, the shrimp-specific IgE assay (f24 ImmunoCAP) contains a mixture of shrimp species, typically including Pandalus borealis (cold-water species) as well as Penaeus and Metapenaeus species (warm-water Indo-Pacific shrimp widely consumed worldwide). These extract-based tests primarily reflect sensitization rather than true clinical allergy and have limited ability to predict reactivity or reaction severity to specific shrimp species. Consequently, OFC with a defined shrimp species remains necessary for definitive diagnosis. To improve diagnostic accuracy, a multitiered approach is increasingly advocated. While sensitive crude extracts serve as effective screens, adding tropomyosin assessment (CRD) significantly enhances specificity and predicts clinical reactivity (14, 21, 22).

In the present study, sIgE to tropomyosin demonstrated the highest specificity, followed by SPT to commercial shrimp extract and whole shrimp sIgE. Diagnostic efficiency was also superior for sIgE to tropomyosin compared with the other modalities. In Thailand, tropomyosin has been identified as a major allergen among shrimp-allergic patients to both Penaeus monodon and Macrobrachium rosenbergii (23, 24). However, component sensitization patterns show geographic variability (21, 25–29). In European and some non-Asian cohorts, tropomyosin is not always the dominant component; instead, other components—such as sarcoplasmic calcium-binding protein (SCP), myosin light chain (Lit v 3), arginine kinase (AK), and other high-molecular-weight proteins—appear to play a more prominent role. In such settings, tropomyosin-specific IgE alone demonstrates lower diagnostic accuracy and is no longer considered a sufficient standalone biomarker (28–30). Therefore, the high specificity of sIgE to tropomyosin and its combination with SPT observed in our Thai cohort should be interpreted as context-specific and may not be directly generalizable to regions with different sensitization profiles.

Our results are consistent with previous studies. Yang et al. (22) reported that the specificity of sIgE to tropomyosin (92.8%) was greater than sIgE to shrimp (75%) and SPT to shrimp extract (64.2%). Serum IgE to tropomyosin had greater diagnostic efficiency (88.5%) compared with whole shrimp-specific IgE (74.2%) or SPT (65.7%). Wai et al. (31) reported low specificities of 28% and 35% for SPT and sIgE to shrimp, respectively, but the specificity of sIgE to rPen a 1 was 90%. Similarly, the results of Thalayasingam et al. (7) demonstrated that SPT using shrimp commercial extract and sIgE to shrimp had specificities of only 37% and 50%, respectively, but the specificity of sIgE to tropomyosin was 85.2%.

For this reason, component-resolved diagnostics (CRD) are recommended as a second-line test. Patients with positive SPT but negative component testing should undergo OFC to confirm or exclude true clinical allergy.

In conventional clinical practice, SPT is usually the first-line investigation. Patients with positive results are frequently advised to avoid shrimp without confirmatory testing. Although prick-to-prick testing using cooked shrimp has been shown to yield high specificity—up to 100% when performed with Penaeus monodon or Macrobrachium rosenbergii—there is a small but definite risk of systemic reactions (∼0.02%), particularly in high-risk patients (6). For this reason, component-resolved diagnostics (CRD) are recommended as a second-line test (32). Patients with positive SPT but negative component testing should undergo OFC to confirm or exclude true clinical allergy.

In our cohort, tropomyosin-specific IgE demonstrated superior specificity (91.9%) compared with extract-based tests; PPVs remained suboptimal (<50%), likely due to low disease prevalence (26%) and potential HDM cross-reactivity (Der p 10 was not assessed). However, combining SPT with sIgE to tropomyosin (rPen a 1) increased diagnostic specificity to 95%. In contrast, combining SPT with shrimp sIgE only modestly improved specificity (70.3%) and remained limited by low sensitivity (46.2%) and moderate NPV (78.8%). Clinically, this implies that nearly one-quarter of patients with negative results on both SPT and shrimp sIgE were still allergic by OFC. Therefore, this strategy cannot safely exclude shrimp allergy in patients with a convincing history. Our results support prior evidence that extract-based SPT and shrimp sIgE have limited predictive value and cannot replace OFC, particularly in high-suspicion cases (5, 7, 10, 16, 27).

The high specificity we observed for combined SPT and sIgE to tropomyosin suggests that this approach may be useful for reducing false-positive diagnoses and unnecessary dietary avoidance. However, it should be noted that our OFC protocol used a cumulative dose of 63 g of boiled shrimp (equivalent to approximately 15 g of shrimp protein), corresponding to a typical serving in Thailand. This dose lies at the lower end of the recommended 15–20 g range (20). Testing with lower challenge doses may increase the risk of false-negative results in individuals with higher reaction thresholds or those requiring specific co-factors (e.g., exercise and NSAIDs) to elicit symptoms. Thus, residual misclassification cannot be completely excluded.

A critical limitation observed across all diagnostic modalities in our study—including SPT, extract-sIgE, and tropomyosin sIgE—was the uniformly poor sensitivity and negative predictive values (NPV). Specifically, tropomyosin sIgE showed a sensitivity of only 23%, meaning it failed to identify nearly 80% of true allergy cases. This finding is in line with an Italian multicenter study, which reported Pen a 1 sensitization in 41% of shrimp-allergic adults (25). The low sensitivity of tropomyosin highlights the relevance of ‘context-specific’ allergen profiles. Sensitization patterns vary significantly by geography and consumption habits. While tropomyosin is often the major allergen in mite-sensitized populations, our data suggest that our cohort may be predominantly sensitized to other heat-stable or labile components not captured by this single test. Minor allergens such as AK, SCP, and myosin light chain are increasingly recognized as clinically relevant triggers, particularly in Asian populations (21, 24, 26–28). Recent studies further indicate that tropomyosin alone is insufficient as a diagnostic marker; recent studies indicate that combining multiple recombinant components (e.g., AK and SCP alongside tropomyosin) can significantly improve diagnostic sensitivity (29). Future research should therefore focus on evaluating multicomponent panels for more accurate diagnosis and tailored to local sensitization profiles to reduce the reliance on OFC.

Several limitations must be acknowledged. First, we employed an open OFC design rather than a double-blind, placebo-controlled OFC, which is considered the gold standard. However, the open method is more feasible in routine practice, and we minimized bias by defining positivity based on objective clinical signs. Moreover, nurses and allergists conducting the OFC were blinded to all index test results. Second, there was a species mismatch between diagnostic tests and the challenge material. The commercial SPT and f24 ImmunoCAP extracts contain mixed shrimp species (e.g., P. monodon, M. barbata, P. borealis, M. joyneri), whereas the OFC used Litopenaeus vannamei. Additionally, the tropomyosin assay employed recombinant Pen a 1 from P. aztecus. In silico analysis by Soto-Muñoz et al. (33) showed very high amino acid sequence identity (95%–100%) between tropomyosin from L. vannamei and P. aztecus, supporting the potential for IgE cross-reactivity. Nevertheless, sequence homology does not guarantee identical allergen expression or clinical relevance, and this remains a methodological limitation. Third, due to the retrospective nature of clinical history taking, the specific shrimp species responsible for the index reaction could not be reliably determined. Given the recognized phenomenon of species-specific prawn allergy, this limitation may partly explain discordance between clinical history and OFC results. Finally, the relatively small number of OFC-positive patients (n = 13) reduces statistical precision and results in wider confidence intervals for sensitivity, PPV, and NPV estimates. These findings therefore require confirmation in larger prospective studies.

In conclusion, conventional diagnostic tools for shrimp allergy—SPT and shrimp sIgE—demonstrate low specificity and limited clinical utility. Measurement of tropomyosin-specific IgE offers significantly higher specificity and improved diagnostic efficiency, either alone or when combined with SPT. This approach may reduce false-positive diagnoses and unnecessary dietary restriction, although OFC remains essential for definitive diagnosis, particularly in patients with compatible clinical histories.