# Pollen-Food Allergy Syndrome: Allergens, Clinical Insights, Diagnostic and Therapeutic Challenges
## 7 PFAS Diagnosis
### Oral Food Challenge (OFC)  
The oral food challenge (OFC) is a gold standard diagnostic procedure for confirming food allergies, including PFAS [98]. While diagnostic tests such as SPT and specific IgE measurements provide valuable insights into sensitization, they may not always correlate with clinical allergy. OFC is designed to confirm whether a specific food triggers an allergic reaction, differentiating between clinically relevant allergies and asymptomatic sensitization. In PFAS, OFC can help:  
* Verify clinical reactions: it determines whether symptoms like oral itching, tingling, or swelling occur after consuming a suspected food [211]. * Differentiate between allergies: OFC distinguishes PFAS, typically caused by labile proteins like PR-10 or profilins, from primary food allergies associated with stable proteins like storage proteins [212]. * Guide dietary management: by identifying tolerable foods, OFC helps avoid unnecessary dietary restrictions, improving patients' quality of life [98]. Oral food challenges (OFC) are categorized into three main types, each with unique advantages and limitations [212]. The open food challenge involves the patient consuming the suspected food in an unblinded manner under medical supervision. This approach is particularly suitable for PFAS, where subjective symptoms like oral itching are expected, and the risk of severe reactions is low. It is simple and cost-effective but may be influenced by patient or clinician bias due to the lack of blinding. In contrast, the single-blind food challenge conceals from the patient whether the food provided is the allergen or a placebo, reducing patient bias and yielding more objective results. The most rigorous method, the double-blind, placebo-controlled food challenge (DBPCFC), ensures that neither the patient nor the clinician knows whether the administered food is the allergen or a placebo. This approach is highly reliable for confirming PFAS and distinguishing it from primary food allergies. However, DBPCFC is time-intensive, resource-demanding, and typically reserved for cases where diagnostic uncertainty remains high [31; 98; 211]. The procedure for an OFC involves the controlled introduction of the suspected food in gradually increasing amounts while closely monitoring the patient for any symptoms. It begins with a pre-challenge evaluation, where a detailed clinical history and prior test results, such as SPT or specific IgE levels, are reviewed to confirm the necessity and safety of the challenge [213]. Contraindications, including uncontrolled asthma or recent severe allergic reactions, are ruled out. Baseline assessments of vital signs, such as heart rate, blood pressure, and oxygen saturation, along with an oral cavity examination, are conducted [213; 214]. Foods are then prepared in their raw form, especially when PFAS is suspected, as heat-labile allergens like PR-10 proteins are often denatured during cooking. Standardized portions are used to ensure accurate dosing. During the incremental dosing phase, the patient consumes small, progressively larger amounts of the food at intervals of 15-30 min under medical supervision. This continues until either a typical serving size is reached or symptoms develop. After the final dose, the patient is observed for 1-2 h to monitor for delayed reactions. Throughout the procedure, symptoms such as oral itching, swelling, or gastrointestinal discomfort are carefully documented to assess the clinical relevance of the suspected food allergen [98]. The outcomes of an OFC in PFAS can vary depending on the patient's response to the suspected food allergen. A positive challenge occurs when symptoms are reproduced, confirming PFAS to the specific food. These symptoms typically include oral itching, mild swelling, and discomfort, characteristic of oral allergy syndrome, and are usually localized without systemic involvement.