What labs and management are recommended for chronic allergies and histamine intolerance?

Laboratory Testing and Management for Chronic Allergies and Histamine Intolerance

For chronic allergies and histamine intolerance, laboratory testing should be guided by clinical history rather than performed as routine panels, with targeted IgE-specific tests being the most valuable for confirming allergic conditions.

Diagnostic Approach for Chronic Allergies

IgE-Specific Testing

• Skin prick testing (SPT) is recommended as the primary test for identifying IgE-mediated allergic reactions 1

  • More sensitive than blood testing
  • Provides direct observation of the body's reaction to specific allergens
  • Results available within 15-20 minutes

• Serum allergen-specific IgE testing (e.g., ImmunoCAP) is an alternative when 1:

  • Skin testing is contraindicated (severe skin conditions like dermatographism or eczema)
  • Patient is on medications that interfere with skin testing (antihistamines)
  • Patient has comorbid conditions that preclude skin testing

When to Test

• Testing should be performed when 1:
  • Patients don't respond to empiric treatment (2-4 weeks of antihistamines and intranasal steroids)
  • The diagnosis of allergic rhinitis is uncertain
  • Identification of specific allergens could affect therapy decisions
  • To aid in titration of therapy

Tests to Avoid

• Do not use the following for diagnosing allergies 1:
  • Total serum IgE (limited diagnostic value)
  • Non-IgE antibody testing (e.g., IgG)
  • Intradermal testing for food allergies
  • Broad panel allergy testing independent of clinical history
  • Atopy patch tests for routine evaluation

Diagnostic Approach for Histamine Intolerance

Histamine intolerance is not IgE-mediated and requires a different diagnostic approach 2, 3:

• No validated laboratory test exists specifically for histamine intolerance
• Diagnosis is primarily clinical and by exclusion of other conditions
• Skin-prick testing and specific IgE to food allergens are typically negative in histamine intolerance 2

Recommended Diagnostic Steps

1. Rule out IgE-mediated allergies first using skin prick tests or serum-specific IgE 4
2. Consider diamine oxidase (DAO) activity measurement - may be lower in patients with histamine intolerance, but has high variability and limited specificity 3
3. Single-blind placebo-controlled histamine challenge may be considered in specialized centers to confirm or exclude the diagnosis 3

Management Recommendations

For IgE-Mediated Allergies

1. First-line therapy: Non-sedating second-generation H1 antihistamines 5

   • Can be increased up to four times the standard dose if necessary
   • Options include cetirizine, desloratadine, fexofenadine, levocetirizine, loratadine 5, 6

2. For inadequate response:

   • Add H2 antihistamines (e.g., famotidine) 5
   • Consider leukotriene receptor antagonists (e.g., montelukast) 5
   • Short course of oral corticosteroids for severe symptoms only 5

3. Avoidance measures:

   • Minimize exposure to identified allergens
   • Avoid aggravating factors like NSAIDs, alcohol, overheating, and stress 5

For Histamine Intolerance

1. Histamine-restricted diet 2:

   • Avoid histamine-rich foods: fish, cheese, hard cured sausages, pickled cabbage, alcoholic beverages (especially red wine)
   • Trial for 4 weeks to assess response

2. Pharmacologic management:

   • H1 antihistamines (same as for allergies) 5
   • Consider H2 antihistamines as adjunctive therapy 5
   • Cooling antipruritic lotions (calamine or 1% menthol in aqueous cream) for symptomatic relief 5

Common Pitfalls to Avoid

• Overreliance on laboratory testing - diagnosis of allergies and histamine intolerance is primarily clinical 1, 5
• Unnecessary extensive testing - investigations should only be performed where suggested by history 5
• Overuse of systemic corticosteroids - should be restricted to short courses for severe cases only 5
• Failure to consider comorbidities - allergies and histamine intolerance can coexist, complicating diagnosis 4
• Misdiagnosis of histamine intolerance - placebo-controlled challenges show that suspected histamine intolerance is disproven in the majority of patients (84.7%) 3

Special Considerations

• Thyroid function testing should be performed in chronic urticaria cases, especially if autoimmune etiology is suspected 1
• For angioedema without wheals, check serum C4 as initial screening for C1 inhibitor deficiency 1
• For physical urticarias, specific challenge testing may be required 1
• For chronic urticaria non-responsive to antihistamines, consider full blood count, ESR, and thyroid autoantibodies 1

By following this targeted approach to testing and management, you can effectively diagnose and treat both chronic allergies and histamine intolerance while avoiding unnecessary testing and treatments.