Phadia’s F256 test is used to detect blood levels of the IgE (antibodies) responsible for allergic reactions to walnuts. The IgE detected in the test may be specific to walnuts or involved in cross allergies with other nuts or birch pollen. The interpretation chart accompanying the result expresses the probability of an allergic reaction to walnuts, but not necessarily the severity of the reaction. Case history (symptoms, relation to meals, etc.) and clinical examination by the physician are essential for a reliable interpretation of the results.
An anti-walnut IgE result (< 0.35 kU/L) indicates that walnuts are probably not responsible for the symptoms reported by the person, but it DOES NOT COMPLETELY RULE OUT THIS POSSIBILITY. All negative and positive results must be interpreted in light of the case history. The double-blind oral food challenge remains the definitive technique for confirming the presence or absence of a food allergy. In certain cases, measuring IgE against specific components of walnuts (anti Jug r1 and anti Jug r3 IgE) can be used to identify a true walnut allergy.