What is the recommended protocol for evaluating a shrimp and scallop allergy through a food challenge?

Protocol for Shrimp and Scallop Food Challenge Testing

The recommended protocol for evaluating shrimp and scallop allergy through food challenge testing should begin with a starting dose of 5 mg for shrimp and gradually increase under strict medical supervision in a facility equipped to handle anaphylaxis. 1

Pre-Challenge Preparation

• Elimination Period: Eliminate suspected foods (shrimp and scallops) from diet for 2-8 weeks prior to testing 1
• Medication Adjustments: Discontinue medications that may interfere with challenge results:
  • Antihistamines: 3-10 days before (depending on type)
  • Oral corticosteroids: 7 days before (if possible)
  • Beta-agonists: 12-24 hours before 1
• Medical Facility Requirements: Must be conducted in a facility with:
  • Onsite medical supervision
  • Emergency medications (especially epinephrine)
  • Resuscitation equipment
  • Personnel experienced in managing anaphylaxis 1, 2

Challenge Protocol Components

Initial Dosing

• Starting dose for shrimp: 5 mg 1
• Starting dose for scallops: 5 mg (based on similar shellfish protocols) 1
• Important consideration: Begin with doses lower than those expected to trigger a reaction 1

Dose Escalation Schedule

1. Begin with 0.1-1% of total challenge food amount
2. Gradually increase dose every 15-30 minutes
3. Continue until reaching a cumulative dose equivalent to a standard age-appropriate portion (2-3 oz of shellfish) 1

Monitoring Parameters

• Vital signs (pulse, blood pressure, oxygen saturation)
• Skin examination (urticaria, angioedema)
• Respiratory assessment (peak flow measurements if appropriate)
• Gastrointestinal symptoms
• Subjective complaints 1

Special Considerations for Shellfish

• Cross-reactivity: Test both shrimp and scallops separately as cross-reactivity between crustaceans (shrimp) and mollusks (scallops) has been documented due to shared tropomyosin allergens (35-39 kD proteins) 3, 4
• Preparation method: Use the same cooking/preparation method that would be consumed in real life, as allergenicity can vary with preparation 1
• Challenge form: For shellfish, the standard portion is 2-3 oz of cooked shellfish 1

Challenge Interpretation

• Positive challenge: Stop at first objective sign of allergic reaction (skin, respiratory, cardiovascular, or gastrointestinal symptoms)
• Subjective symptoms: If only subjective symptoms occur (throat itching, mouth itching), observe for resolution before administering next dose 1
• Negative challenge: If patient tolerates full challenge dose without symptoms, shellfish allergy can be ruled out 1

Post-Challenge Management

• Observation period: Monitor for at least 4-6 hours after challenge completion, as delayed reactions can occur 2
• Positive reaction management:
  • Administer epinephrine 0.01 mg/kg (max 0.3-0.5 mg) IM for severe reactions
  • Provide antihistamines for mild-moderate symptoms
  • Position patient supine with legs elevated if experiencing hypotension 2
• Documentation: Record all symptoms, timing, and treatments administered 2

Common Pitfalls to Avoid

• Insufficient starting dose: Starting with too high a dose can trigger severe reactions
• Inadequate monitoring: Failing to observe for delayed reactions
• Improper preparation: Not using the same cooking method that would be consumed in real life
• Ignoring cross-reactivity: Not testing both shellfish separately despite potential cross-reactivity 1, 3, 4
• Delayed epinephrine administration: Not promptly treating anaphylactic reactions 2

Food challenges remain the gold standard for diagnosing shellfish allergy, as they provide definitive evidence of clinical reactivity beyond what skin or blood testing can offer 1, 5.