What are the different types of allergy testing methods?

Types of Allergy Testing

The primary allergy testing methods are skin prick testing (first-line), intradermal testing (when additional sensitivity needed), and allergen-specific IgE blood testing (when skin testing contraindicated), with patch testing reserved for contact dermatitis evaluation. 1, 2

Primary IgE-Mediated Testing Methods

Skin Prick/Puncture Testing

Skin prick testing should be your first-line diagnostic approach due to superior sensitivity (>80%), immediate results within 15-20 minutes, and lower cost compared to blood testing. 1, 2

• The test introduces allergen into the epidermis, causing mast cell degranulation and histamine release that produces a visible wheal and flare reaction. 1
• Results are read at 15-20 minutes by measuring wheal and erythema diameters, comparing against positive (histamine) and negative (saline) controls. 1
• Document all medications taken within the past week, as antihistamines and tricyclic antidepressants suppress skin test responses and cause false negatives. 1
• Use standardized allergen extracts when available to ensure reproducibility. 1
• The back or volar forearm are acceptable testing sites, though the back provides more surface area for multiple allergens. 1, 3

Intradermal/Intracutaneous Testing

Use intradermal testing when skin prick testing is negative but clinical suspicion remains high, or when increased sensitivity is required for specific allergens. 1, 2

• This involves injecting 0.01-0.02 mL of allergen into the dermis, providing greater sensitivity than prick testing but lower specificity. 1, 3
• Critical safety consideration: Six fatalities have been reported from intradermal inhalant testing, five occurring in asthmatics who did not receive prick testing first. 1, 2
• Always perform prick testing before intradermal testing to minimize anaphylaxis risk, especially in asthmatic patients. 1

Allergen-Specific IgE Blood Testing

Choose blood testing over skin testing when: widespread eczema or severe dermatographism is present, antihistamines cannot be discontinued, patient is on β-blockers, or there is unusually high anaphylaxis risk. 1, 2

• The test uses immunoassays where serum is incubated with allergen absorbed on a solid phase, then bound IgE is measured with labeled anti-IgE antibodies. 1
• Blood testing has 70-75% sensitivity compared to skin prick tests, making it less sensitive but still clinically useful. 2
• Key advantage: No risk of anaphylaxis and results are not affected by antihistamine use. 1
• Do not order total IgE or IgG testing for allergy diagnosis—these provide no useful information for managing allergic disease. 1

Interpretation Principles for IgE Testing

Both skin and blood tests measure sensitization, not clinical allergy—negative predictive value exceeds 95%, but positive predictive value is only 40-60%. 1, 4

• Negative results effectively rule out IgE-mediated allergy. 1
• Positive results require clinical correlation: larger wheals (>8-10 mm) and higher specific IgE levels increase likelihood of true clinical reactivity. 1
• Common pitfall: Patients with positive tests may tolerate the allergen without symptoms—sensitization does not equal clinical allergy. 5

Component-Resolved Diagnostics (CRD)

Order CRD as second-line testing only when initial skin prick or whole allergen IgE results are equivocal, not as first-line testing. 2

• CRD identifies specific allergenic proteins within foods, helping distinguish genuine food allergy from cross-reactive pollen sensitization. 2
• Positive CRD to storage proteins indicates genuine sensitization with high likelihood of clinical allergy and potential for severe reactions. 2
• This testing can reduce the need for oral food challenges by nearly two-thirds when used appropriately. 2

Patch Testing for Delayed Hypersensitivity

Patch testing is the diagnostic standard for contact dermatitis (type IV hypersensitivity), not for routine food or inhalant allergy evaluation. 1, 6

• Allergen-soaked pads are applied to unbroken skin (typically the back) under occlusion for 48 hours, with readings at 48 and 72 hours. 1
• The test has 70-80% sensitivity and specificity for contact allergens. 1
• Atopy patch testing (APT) for food allergy is not recommended for routine use—it lacks standardized reagents, shows highly variable sensitivity/specificity, and provides no significant clinical value beyond skin prick or IgE testing. 1

Food Allergy-Specific Testing Approach

For children under 5 years with moderate-to-severe atopic dermatitis, consider limited food allergy testing (cow's milk, eggs, wheat, soy, peanut) only if: persistent disease despite optimized topical therapy, reliable history of immediate reaction after specific food ingestion, or both. 1

• In older children and adults, test tree nuts, shellfish, and fish based on clinical history and population prevalence. 1
• Avoid broad panel allergy testing without specific clinical history—this leads to false positives and unnecessary dietary restrictions. 1

Oral Food Challenge: The Gold Standard

When diagnosis remains uncertain after testing, oral food challenge is the definitive diagnostic test, though it carries risk of provoking significant reactions. 1, 4

• Double-blind, placebo-controlled food challenges provide the highest diagnostic certainty but are time-consuming and resource-intensive. 1, 4
• Reserve challenges for: confirming tolerance development, evaluating equivocal test results, or when history and testing are discordant. 1

Tests to Avoid

Do not use these unproven methods: IgG food antibody testing, provocation/neutralization testing, applied kinesiology, cytotoxic tests, or electrodermal testing. 1, 7

• These lack scientific validation and may lead to misdiagnosis and unnecessary dietary restrictions. 7