Biomarker: F302-IgE Tangerine

Overview

F302-IgE Tangerine refers to evaluation of IgE sensitization to tangerine or mandarin, the fruit of Citrus reticulata. Tangerine is an ingested plant-food allergen and contains characterized allergenic proteins including Cit r 3, a nonspecific lipid-transfer protein. Human reports describe reactions ranging from oral allergy symptoms to urticaria, respiratory symptoms, and rare anaphylaxis after ingestion. Serum-specific IgE testing may help evaluate suspected IgE-mediated reactions when interpreted with the exposure history and clinical symptoms, but a positive result indicates sensitization and does not by itself establish clinical allergy.

Clinical Use Cases

Evaluation of suspected IgE-mediated food allergy: Supports investigation when symptoms occur soon after eating tangerine or foods containing tangerine.
Serum-specific IgE assessment: Measures circulating IgE antibodies that recognize tangerine allergen extracts in a blood sample.
Investigation of exposure-associated symptoms: May be considered in patients with reproducible oral itching, urticaria, angioedema, wheezing, gastrointestinal symptoms, or other immediate symptoms after tangerine ingestion.
Assessment with clinical history: Results should be interpreted alongside the timing, reproducibility, amount consumed, food preparation, co-factors, and symptoms associated with exposure.
Evaluation of cross-reactive sensitization: May help assess whether sensitization to tangerine is part of a broader citrus or plant-food sensitization pattern, particularly involving lipid-transfer proteins or profilin.
Diagnostic clarification: If the history and serum-specific IgE results do not establish whether the patient is clinically reactive, an allergist may consider skin testing or a medically supervised oral food challenge. Oral food challenge remains the most direct method for confirming clinical food allergy when appropriate.

Specimen Types

Serum: Commonly used for measurement of tangerine-specific IgE.
Plasma or blood sample: May be accepted by some laboratory platforms for in-vitro allergen-specific IgE analysis, depending on the assay.

Measurement Methods

Allergen-specific IgE testing: In-vitro immunoassays measure IgE antibodies in serum or blood that bind to tangerine or mandarin allergen extracts. Results support assessment of sensitization and must be interpreted with clinical history.
Component-resolved diagnostics: Testing for IgE directed against individual molecular allergens may help characterize sensitization to components such as Cit r 3, a nonspecific lipid-transfer protein. Molecular testing is not available or clinically validated for every tangerine component and does not independently confirm clinical allergy.
Skin-prick or prick-to-prick testing: These methods may provide additional clinical information, particularly when testing with fresh fruit is relevant, but they assess sensitization in vivo and should be directed by an allergy-focused history.
Oral food challenge: A medically supervised challenge may be used when diagnosis remains uncertain after history and sensitization testing. It is a clinical procedure rather than a blood-based laboratory measurement and should not be performed without appropriate medical supervision.

Test Preparation and Influencing Factors

Preparation: Allergy blood testing generally requires no fasting or other special preparation.
Medications: Antihistamines generally do not alter serum-specific IgE measurement, although they can interfere with skin-prick testing. Patients should disclose all medications and should not stop prescribed treatment unless instructed by a healthcare professional.
Clinical history: Testing should be targeted to foods suspected from the exposure history rather than performed as an unrelated broad panel. The history determines the pretest probability and is central to interpretation.
Sensitization versus allergy: A detectable tangerine-specific IgE result demonstrates immunologic sensitization. It does not prove that eating tangerine will cause symptoms or predict reaction severity.
Total IgE: Total serum IgE should not be used alone to diagnose food allergy. Very high total IgE, including in severe atopic disease, may be associated with multiple positive specific-IgE results of uncertain clinical relevance.
Age and assay characteristics: Specific-IgE concentrations and their clinical predictive value can vary with age, assay characteristics, allergen extract composition, and the population tested. Class or concentration should not be treated as a direct measure of reaction severity.
Cross-reactive sensitization: IgE binding to homologous proteins from other citrus fruits, pollens, or plant foods may contribute to a positive result without clinically meaningful reaction to tangerine.
Timing of testing: Testing should be interpreted in relation to the suspected reaction and exposure history. A negative extract-based result may not exclude allergy if the relevant allergen is absent or poorly represented in the test preparation.

Cross-Reactivity

Other citrus fruits: Cit r 3 is a nonspecific lipid-transfer protein found in tangerine and is related to lipid-transfer proteins in orange, lemon, and other citrus fruits. Human studies have demonstrated IgE cross-reactivity among citrus lipid-transfer proteins.
Peach and other plant foods: Citrus lipid-transfer proteins can show IgE cross-reactivity with nonspecific lipid-transfer proteins from peach and other plant foods. This may occur as part of a broader lipid-transfer-protein sensitization pattern.
Profilin-related sensitization: Human clinical research has associated profilin sensitization with reactions or oral allergy symptoms to several plant foods, including citrus fruits. Profilin is a pan-allergen, and a positive result may reflect cross-sensitization rather than clinically important allergy to every related food.
Germin-like proteins: A mandarin-associated anaphylaxis report identified sensitization to Cit r 3 and also to other citrus components, including a germin-like allergen from orange. This represents evidence from an individual clinical case and does not establish that all tangerine reactions involve these proteins.
Clinical relevance: Immunologic cross-reactivity does not mean that a person sensitized to one citrus fruit, lipid-transfer protein, or profilin will react to every citrus or plant food. Individual foods should be evaluated according to the clinical history and, when necessary, supervised challenge.