Phadia’s F304 test is used to detect blood levels of the IgE (antibodies) responsible for allergic reactions to crawfish. Although some people may be allergic only to crawfish, this crustacean has allergens in common with shrimp, lobster, crayfish and Norway lobster. Co-allergies to molluscs and other seafood are also possible. The interpretation chart accompanying the result expresses the probability of an allergic reaction to crawfish (and possibly other crustaceans), 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-crawfish IgE result (< 0.35 kU/L) indicates that crawfish are probably not responsible for the symptoms reported by the person, but it DOES NOT COMPLETELY RULE OUT THIS POSSIBILITY. Both negative and positive results must be interpreted in light of the case history. In more complex cases, the double-blind oral food challenge under medical supervision remains the definitive technique for confirming the presence or absence of a crawfish allergy. Unlike milk and egg white allergies, which many children outgrow, the hypersensitivity to crawfish and other crustaceans tends to develop in adulthood and persist for life.