Combined shellfish and finfish allergy blood testing is used to evaluate whether a person is allergic to both shellfish and finfish, which are distinct food groups with different allergens. A person can be allergic to one group (shellfish or finfish) without being allergic to the other, but some individuals may be allergic to both. These tests help identify specific immune responses to the proteins found in various fish and shellfish species.

Understanding Shellfish vs. Finfish Allergies

  • Shellfish: Includes two main groups — crustaceans (shrimp, crab, lobster) and molluscs (clams, mussels, oysters, squid, and scallops).
  • Finfish: Includes all species of finned fish like salmon, tuna, cod, haddock, and tilapia.

Allergies to shellfish and finfish involve different proteins, though some people may experience both due to separate sensitisations.

Types of Blood Tests for Combined Shellfish/Finfish Allergy

  1. Specific IgE (sIgE) Testing:
    • This test measures specific IgE antibodies to individual shellfish and finfish proteins.
    • For shellfish, the test checks for IgE antibodies to:
      • Crustaceans (shrimp, Prawn)
      • Molluscs (squid, scallops)
    • For finfish, the test checks for IgE antibodies to different fish species:
      • Salmon
      • Tuna
      • Cod
    • These results help pinpoint which specific shellfish or fish are causing allergic reactions.
  2. Component-Resolved Diagnostics (CRD):
    • CRD allows for a more detailed look at the specific protein components (allergens) that may be causing the allergic reaction.
    • In shellfish, the main allergen is tropomyosin, a protein found in the muscle tissue of crustaceans and molluscs. Cross-reactivity within shellfish species is common due to the presence of this protein.
    • In finfish, the main allergens are parvalbumins, which are heat-resistant proteins in the muscle of finfish. This test can help differentiate which protein is causing the reaction and predict cross-reactivity between different fish species.
  3. Cross-Reactivity Testing:
    • Cross-reactivity between different species of shellfish is common (e.g., shrimp and crab) due to shared allergens, especially tropomyosin.
    • Cross-reactivity between shellfish and finfish is rare because the proteins involved in each allergy are different (tropomyosin vs. parvalbumin). However, testing both can help clarify sensitivities.
  4. Total IgE Test:
    • This test measures the overall IgE level in your blood and can indicate a general tendency toward allergic responses. While helpful in understanding allergic predisposition, it does not specify which allergens are causing reactions.

Testing Procedure

  1. A blood sample is drawn and sent to a lab.
  2. The lab tests for the presence of specific IgE antibodies to shellfish and finfish allergens.
  3. Results are given as numerical values (ranging from Class 0 to Class 6), with higher levels indicating a stronger likelihood of an allergic reaction to the tested allergen.

Considerations in Diagnosis

  • Cross-Contact: Even if a person is allergic to shellfish and not finfish (or vice versa), they should be cautious of cross-contact in restaurants or food preparation, as these foods are often prepared in the same environments.
  • Multiple Sensitizations: Some individuals may have multiple food allergies, so testing for both shellfish and finfish is beneficial when allergic reactions are unclear or have multiple triggers.

Diagnosis and Management

  • Combined Diagnosis: A diagnosis is made based on specific IgE levels, clinical symptoms, and sometimes an oral food challenge. The results will guide the person in managing their diet and avoiding allergens.
  • Treatment: Avoidance of the specific shellfish or finfish causing reactions is the primary management approach. In severe cases, patients may need to carry an epinephrine auto-injector (EpiPen) for emergency use.

By using Combined shellfish and finfish allergy blood testing, healthcare providers can get a clearer picture of which foods are causing allergic reactions and recommend the best dietary and safety strategies. If you suspect a combined allergy, consultation with an allergist is essential for proper testing and management.

Results – 2 days from Laboratory receiving sample

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