Biomarker: F343-IgE Raspberry

Overview

Raspberry (Rubus idaeus L.) is a plant-derived fruit and a potential food allergen. F343 refers to measurement of allergen-specific IgE directed toward raspberry extract in blood or serum. Identified raspberry IgE-reactive proteins include Rub i 1, a PR-10 protein; Rub i 3, a lipid-transfer protein; class III chitinases; and a cyclophilin. Raspberry exposure most commonly occurs through eating fresh or processed fruit, although clinically reported reactions are uncommon. Testing may help evaluate suspected IgE-mediated reactions when interpreted with the exposure history and, when necessary, additional allergy testing or a medically supervised oral food challenge.

Clinical Use Cases

Evaluation of suspected IgE-mediated raspberry allergy: Serum-specific IgE testing may help identify sensitization in a patient with an immediate reaction after eating raspberry.
Investigation of exposure-associated symptoms: Testing may be considered for symptoms such as oral itching, urticaria, respiratory symptoms, gastrointestinal symptoms, or anaphylaxis occurring after raspberry exposure. Documented raspberry reactions include rare immediate systemic reactions, including anaphylaxis.
Serum allergen-specific IgE assessment: F343 testing measures IgE antibodies that bind to raspberry extract in a blood sample. A positive result indicates sensitization, not necessarily symptomatic clinical allergy.
Assessment with clinical history: Results should be interpreted with the timing, reproducibility, amount and form of raspberry consumed, co-factors, and objective symptoms.
Evaluation of cross-reactive sensitization: Raspberry-specific IgE may reflect recognition of proteins shared with other Rosaceae fruits, birch pollen-related PR-10 proteins, lipid-transfer proteins, or carbohydrate determinants.
Confirmation of clinical relevance: When the history and testing are inconclusive, a supervised oral food challenge may be used by an appropriately trained clinician. Serum-specific IgE testing alone does not establish food allergy.

Specimen Types

Serum or blood: Venous blood, usually analyzed as serum, is used for measurement of raspberry-specific IgE.

Measurement Methods

Allergen-specific IgE testing: An in-vitro immunoassay measures circulating IgE antibodies that bind to raspberry extract. The result supports assessment of sensitization but must not be interpreted as a stand-alone diagnosis.
Component-resolved diagnostics: Testing for IgE to individual raspberry proteins such as Rub i 1 or Rub i 3 may provide additional information when clinically available and validated. Component testing is intended to complement, not replace, the clinical history and whole-extract testing.
Skin-prick testing: Skin-prick testing may be used as an additional assessment of IgE sensitization, but it is not a blood-based measurement and does not independently confirm clinical allergy.
Oral food challenge: A medically supervised oral food challenge assesses clinical reactivity directly and is used when the diagnosis remains uncertain after history and sensitization testing.

Test Preparation and Influencing Factors

Fasting: Fasting is generally not required for serum-specific IgE blood testing unless other blood tests collected at the same time require it.
Medications: Antihistamines generally do not prevent measurement of serum-specific IgE, although they can affect skin-prick testing. Medication decisions should be made with the treating clinician.
Clinical timing: Testing should be interpreted in relation to the timing of symptoms and raspberry exposure. A result obtained after a reaction does not by itself establish that raspberry caused the reaction.
Total IgE concentration: Total serum IgE should not be used alone to diagnose food allergy. Very high total IgE may complicate interpretation of some specific-IgE results.
Age and clinical context: Predictive values vary with age, population, assay, and pretest probability. Raspberry-specific IgE concentration should not be used alone to predict reaction severity.
Cross-reactive sensitization: IgE binding to homologous proteins or cross-reactive carbohydrate determinants may produce a positive F343 result without clinically meaningful reactions to raspberry.
Sensitization versus allergy: A positive result indicates immunologic sensitization. Clinical allergy requires compatible symptoms after exposure, with oral food challenge used when objective confirmation is needed.
Assay differences: Reference ranges, reporting units, detection limits, and extract composition can differ among laboratory methods. Results should be interpreted using the reporting laboratory’s method-specific information.

Cross-Reactivity

Rosaceae fruits: Rub i 1 and Rub i 3 show sequence similarity to related proteins in apple, cherry, peach, and other Rosaceae fruits, including Mal d 1, Mal d 3, Pru av 1, Pru av 3, Pru p 1, and Pru p 3.
PR-10 proteins: Rub i 1 is a PR-10 protein related to Bet v 1, the major birch-pollen allergen. This relationship may contribute to IgE cross-sensitization between birch pollen and some plant foods, although sensitization does not necessarily cause symptoms after raspberry consumption.
Lipid-transfer proteins: Rub i 3 is a lipid-transfer protein related to lipid-transfer allergens in other fruits, including peach. Lipid-transfer-protein sensitization has been reported in patients with raspberry reactions, but a positive result to a related lipid-transfer protein does not by itself establish raspberry allergy.
Class III chitinase and carbohydrate determinants: Raspberry class III chitinase reacted with IgE in more than 80% of sera from the sensitized patients studied and contained cross-reactive carbohydrate determinants. This finding may contribute to immunologic cross-reactivity or positive extract-based testing without proving clinically significant raspberry allergy.
Clinical relevance: Immunologic cross-reactivity is more common than clinically symptomatic cross-reactivity. Symptoms must be evaluated separately for each food and in relation to the patient’s exposure history.