How do I diagnose food sensitivity?

Diagnosing Food Sensitivity

The most accurate method to diagnose food sensitivity is through a structured approach of elimination diet followed by controlled food challenges, as there are no reliable in vitro or skin tests with adequate sensitivity and specificity for non-IgE-mediated food intolerances. 1

Understanding Food Sensitivity vs. Food Allergy

Food reactions can be categorized into two main types:

1. Food Allergy (Immune-mediated)

   • IgE-mediated: Rapid onset (minutes to hours), can cause anaphylaxis
   • Non-IgE-mediated: Delayed onset (hours to days), includes conditions like FPIES, allergic proctocolitis, and eosinophilic disorders

2. Food Intolerance (Non-immune-mediated)

   • Caused by pharmacologic, toxic, or metabolic properties of food
   • Examples: lactose intolerance, reactions to food additives like sulfites 1

Diagnostic Algorithm for Food Sensitivity

Step 1: Detailed Clinical History

• Document specific symptoms and their timing in relation to food consumption
• Identify suspected trigger foods
• Note pattern of symptoms (immediate vs. delayed)
• Record symptom severity and consistency of reactions 1

Step 2: Determine Appropriate Testing Path

Based on symptom presentation:

For Suspected IgE-Mediated Food Allergy:

• Skin prick tests (SPT) or serum-specific IgE tests are appropriate
• Positive tests indicate sensitization but not necessarily clinical allergy
• Neither test should be used for screening without clinical suspicion 1

For Suspected Non-IgE-Mediated Food Sensitivity:

• Elimination diet is the primary diagnostic tool
• Complete elimination of suspected trigger foods for 2-4 weeks 2, 3
• Document symptom improvement during elimination period 2

Step 3: Confirmation Testing

For IgE-Mediated Food Allergy:

• Oral food challenge (OFC) remains the gold standard
• Should be performed in a controlled medical setting with emergency equipment available 1, 4
• Component-resolved diagnostics may be helpful for specific foods (e.g., Ara h 2 for peanut) 1

For Non-IgE-Mediated Food Sensitivity:

• Reintroduction of eliminated foods one at a time
• Monitor for return of symptoms
• Double-blind placebo-controlled food challenge is the most rigorous approach 2, 5

Tests to Avoid

• Unvalidated or unproven tests that lack scientific evidence:
  • IgG or IgG4 testing (inconsistent results, poor reproducibility) 5
  • Applied kinesiology or muscle testing
  • Vega testing or electrodermal testing
  • Cytotoxic testing
  • Hair analysis 5

Special Considerations

Specific Non-IgE-Mediated Conditions:

• Food Protein-Induced Enterocolitis Syndrome (FPIES):

  • Diagnosis based on medical history and oral food challenge
  • Typically presents with vomiting, diarrhea, and in some cases shock 1-4 hours after ingestion 1

• Allergic Proctocolitis (AP):

  • Diagnosed by medical history, resolution with food elimination, and recurrence with challenge
  • Presents as blood-streaked stools in otherwise healthy infants 1

• Sulfite Sensitivity:

  • Requires elimination diet and controlled challenge
  • Skin tests have poor sensitivity 2

Follow-Up Management

• Once food sensitivity is confirmed, provide specific avoidance guidance
• Consider periodic re-evaluation as many food sensitivities resolve over time
• For children with food allergies, follow-up challenges are warranted to determine when the condition has resolved 1

Common Pitfalls to Avoid

• Relying solely on test results without clinical correlation
• Over-testing leading to unnecessary dietary restrictions
• Failing to distinguish between sensitization and clinical allergy
• Using unvalidated alternative testing methods 1, 5

Remember that elimination diets should be nutritionally adequate and supervised by healthcare professionals, especially for children or when multiple foods are eliminated.