Lab

Allergy Screening

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Allergy Screening, Allergy Test

  • See Also
  1. Patch Testing
  2. Skin Testing
  3. RadioAllergoSorbent Test
  4. Regional Allergy Screening
  • Indications
  1. Refractory Allergic Rhinitis
  2. Refractory Asthma
  3. Food Allergy or drug allergy suspected
  4. Insect sting allergy suspected
  5. Angioedema
  6. Contact Dermatitis
  • Types
  • In Vivo Tests
  1. Hypersensitivity Skin Testing (Skin Prick Test or Intradermal Test)
    1. IgE immediate Type 1 Hypersensitivity Reaction
  2. Patch Testing
    1. Contact Dermatitis (Delayed Type 4 Hypersensitivity, T Cell-mediated response)
  3. Oral Food Challenge
    1. IgE immediate Type 1 Hypersensitivity Reaction
    2. Indicated in Food Allergy
  • Types
  • In Vitro Tests
  1. Allergen Specific IgE Antibody Measurement (via ImmunoCAP or RadioAllergoSorbent Test)
    1. IgE immediate type Hypersensitivity
    2. Indicated in patients at risk for severe Anaphylaxis with allergan exposure
    3. Not impacted by Dermatographism or dermatitis (and not altered by Antihistamine use)
  • Devices
  1. Morrow-Brown Needle
  2. Multi-Test (Lincoln Diagnostics)
  3. Quintest (Bayer)
  4. Modified RadioAllergoSorbent Test (RAST)
  5. Quidel finger stick device
  • Approach
  1. Inhalant Allergy
    1. See Regional Allergy Screening
    2. Skin Testing is preferred (most cost-effective)
    3. IgE specific Antibody testing panels are available for each U.S. region
  2. Food Allergy
    1. Food Allergy testing has a high False Positive Rate and should only be performed based on a specific history
    2. Start with a history of common Food Allergy causes
      1. Hen's eggs, cow's milk or peanuts (85% of food allergies in children and teens)
      2. Fish or shellfish
      3. Soy
      4. Tree nuts (e.g. cashews, walnuts)
      5. Wheat allergy (gluten sensitivity, Celiac Sprue)
    3. Patient should eliminate food they suspect as allergan
      1. If symptoms improve after food elimination, then consider Allergy Testing for that food item
    4. Skin Testing or IgE specific Antibody testing
      1. High Negative Predictive Value
      2. Positive test results are of limited value (high False Positive Rate)
        1. Many patients may tolerate food items despite a positive test
        2. Avoid broad-based Food Allergy panel screening
    5. Food challenge
      1. Confirms negative Allergy Testing
  3. Insect Allergy
    1. Testing indicated in suspected Stinging InsectAnaphylaxis or diffuse skin reactions
    2. Test via Skin Testing or IgE specific Antibody testing
    3. Test for most common Insect allergans (e.g. fire ants, honey bees, yellow hornets, yellow jackets, wasps)
    4. Immunotherapy for those at high risk for severe future reactions
    5. Obtain Serum Tryptase level
      1. Evaluate for Mast Cell activation syndrome if Serum Tryptase >11.5 ng/ml
  4. Antibiotic allergy (esp. Penicillin Allergy)
    1. Only 1-10% of self-reported Penicillin Allergy have an abnormal skin test
    2. Penicillin Skin Testing has a Negative Predictive Value >95%
      1. Often confirmed with a monitored oral challenge in allergy clinic
      2. Penicillins may safely be prescribed after negative skin test
  • References
  1. (1999) NPI Allergy Testing Conference, Las Vegas
  2. Bright (2023) Am Fam Physician 108(2): 159-65 [PubMed]
  3. Chang (2018) Am Fam Physician 98(1): 34-9 [PubMed]
  4. James (2002) Am Fam Physician 66(4):621-6 [PubMed]