# Pollen-Food Allergy Syndrome: Allergens, Clinical Insights, Diagnostic and Therapeutic Challenges
## 7 PFAS Diagnosis
### Component-Resolved Diagnostics (CRD)  
Component-resolved diagnosis (CRD) is a cutting-edge diagnostic tool that can identify specific allerggenic proteins to which a patient is sensitized. Unlike traditional diagnostic methods, such as whole allergen extracts used in SPT or specific IgE tests, CRD focuses on individual allergenic molecules. This approach is particularly valuable in PFAS, where cross-reactivity between structurally similar proteins in pollens and plant-based foods is a key feature [138]. By identifying the precise protein responsible for sensitization, CRD provides greater diagnostic accuracy, enabling personalized management strategies for patients.  
CRD relies on advanced molecular diagnostic platforms that measure specific IgE against individual allergenic components, enabling precise identification of sensitivities that traditional methods using whole allergen extracts may miss. While there are several platforms available for component-resolved diagnostics, ImmunoCAP, ISAC, and ALEX are among the most widely used. These platforms employ advanced technologies to offer valuable insights into the mechanisms of allergic responses and cross-reactivity [119,137,138].  
ImmunoCAP (Thermo Fisher Scientific, Uppsala, Sweden) is a singleplex diagnostic assay that tests for specific IgE to a single allergen or allergenic component per test [199]. It uses a solid-phase system where allergens are immobilized on a cellulose sponge matrix. This platform provides quantitative results expressed in kU/L, allowing clinicians to assess the degree of sensitization and its clinical significance. ImmunoCAP is highly sensitive and specific, making it ideal for targeted testing and long-term monitoring of IgE levels [200]. However, its singleplex nature means it is less efficient for patients with complex allergy profiles requiring multiple tests [190].  
ISAC (Immuno Solid-Phase Allergen Chip; ThermoFisher Scientific, Waltham, MA, USA) is a multiplex diagnostic platform that tests for IgE to over 100 allergenic components simultaneously [201]. It uses a microarray chip with purified allergens immobilized on its surface. Requiring only a small amount of serum, ISAC provides a semi-quantitative profile of sensitization, making it particularly useful for patients with polysensitization or unclear allergic triggers. Its ability to test for panallergens like PR-10 proteins, profilins, and LTPs helps identify cross-reactivity patterns. However, ISAC results are semi-quantitative, meaning they are less precise than ImmunoCAP's fully quantitative measurements [202].  
ALEX (Allergy Xplorer, MacroArray Diagnostics GmbH (MADx), Vienna, Austria) is another multiplex diagnostic platform that tests for IgE against more than 300 allergens, combining whole allergen extracts and molecular components. Unlike ISAC, ALEX includes cross-reactivity inhibition, which minimizes false positives from panallergens like profilins and CCDs (cross-reactive carbohydrate determinants) [201]. This feature enhances specificity and makes ALEX particularly valuable for distinguishing primary sensitivities from cross-reactivity [203]. While results are semi-quantitative, ALEX integrates comprehensive allergen profiling with user-friendly data presentation, making it a powerful tool for complex allergy cases [204].  
These diagnostic methods, each with its distinct strengths and limitations, play a complementary role in the comprehensive evaluation of allergies. By leveraging their unique features, clinicians can achieve a more accurate and tailored approach to diagnosis. For an in-depth comparison of their characteristics, practical applications, and limitations, please refer to Table 3 below.