Diagnostic considerations when evaluating fish and shellfish allergy

Concern	Implication/approach
Clinical cross-reactivity	The rate of serologic (positive test) cross-reactivity exceeds the rate of true clinical reactivity, but both are high in seafood allergy. Therefore, caution is needed (evaluations with tests for IgE and possibly oral food challenges).
Overlap of symptoms with nonallergic seafood reactions	Spoilage of seafood most typically results in gastrointestinal reactions that are not consistent and do not mimic allergy (differentiated by history). However, spoilage of dark meat fish (scombroid poisoning) could result in symptoms that mimic allergy (pruritus, flushing).
Reactions may vary	Inconsistencies in reactions to fish could be attributable to manner of cooking or to which parts of the fish are eaten. Reduced digestion of fish protein is also a variable that could be altered if a patient takes antacid medication. These points should be examined in the history and considered during allergy testing.
Reactions may be attributed to seafood, but caused by other allergens	If a reaction occurs during a meal, ingredients must be reviewed to determine other causes (spices, etc). Other fish-related foods (caviar) or contaminants (parasites, such as Anisakis) could be causal.

IgE: immunoglobulin E.

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