What allergy testing can be done in a primary care setting for a patient with suspected allergies?

Allergy Testing Available in Primary Care

In primary care, you can perform serum-specific IgE blood testing for suspected allergies, which is the most practical option since it requires no special equipment, is unaffected by medications, and can be ordered through standard laboratories. 1, 2

When to Order Allergy Testing

Perform specific IgE testing only when:

• Patients fail 2-4 weeks of empiric treatment with antihistamines and intranasal steroids 3, 1
• The diagnosis is uncertain despite clinical presentation 3, 1
• Identifying the specific allergen will change management (e.g., guide immunotherapy, allergen avoidance, or medication adjustments) 3, 1

Do not order allergy testing:

• As a screening tool without clinical suspicion of allergic disease 3
• Based solely on patient request without supporting symptoms 3
• When history and physical examination clearly indicate non-allergic etiology 3

Testing Modalities Available in Primary Care

Serum-Specific IgE Blood Testing (Preferred for Primary Care)

• This is your go-to test because it requires only a blood draw, results are unaffected by antihistamines or other medications, and interpretation is straightforward 4, 2, 5
• Order testing only for allergens suspected based on clinical history—avoid broad "allergy panels" that lead to false-positive results 3, 2
• Negative predictive value exceeds 95%, but positive predictive value is only 40-60%, meaning positive results require clinical correlation 1

Skin Prick Testing (Requires Referral or Special Training)

• While skin prick testing is more sensitive (>80%) and provides immediate results, it requires specialized training, equipment, and emergency preparedness for potential anaphylaxis 3, 1, 2
• Most primary care settings lack the infrastructure for skin testing, making referral to an allergist more practical 6, 7
• Antihistamines must be discontinued for specific periods before testing (intranasal steroids can continue) 4, 8

Critical Testing Pitfalls to Avoid

Never order these tests—they provide no diagnostic value:

• Total serum IgE levels (not diagnostic of specific allergies) 3, 1
• IgG or IgG4 food antibody testing (no evidence base) 3, 1
• Intradermal food testing (not recommended) 3
• Atopy patch testing for non-contact allergies 3

Interpreting Results

A positive test indicates sensitization (presence of allergen-specific IgE), not necessarily clinical allergy 1, 2

• You must correlate positive results with the patient's symptom history and exposure patterns 1, 2
• A patient can have positive IgE to an allergen but tolerate exposure without symptoms 1
• Conversely, a negative test effectively rules out IgE-mediated allergy to that allergen (>95% negative predictive value) 1

Special Considerations by Allergy Type

Allergic Rhinitis

• Test only after failed empiric treatment with second-generation antihistamines and intranasal corticosteroids for 2-4 weeks 3, 1
• Order specific IgE for suspected environmental allergens based on seasonal patterns and exposure history 3, 2

Food Allergies

• Start with elimination diet of the suspected food for 2-4 weeks based on history alone 3
• If elimination is ineffective or diagnosis remains uncertain, order specific IgE testing for the suspected foods 3
• Refer to allergist for oral food challenge if testing is equivocal or to confirm diagnosis before long-term elimination 3
• Testing without clinical suspicion yields 50-90% false-positive results 3

Insect Sting Anaphylaxis

• Patients with anaphylactic reactions to insect stings should undergo specific IgE testing or be referred for skin testing 2

Drug Allergies

• Penicillin skin testing has high negative predictive value and can be performed by trained providers when penicillin is indicated with limited alternatives 2
• Testing for other drug allergies has less established sensitivity/specificity—consider referral 2

When to Refer to Allergist

Refer when:

• You lack access to reliable specific IgE testing 1, 7
• Patient requires oral food challenge to confirm food allergy diagnosis 3
• Patient is candidate for immunotherapy based on inadequate response to pharmacotherapy 3
• Diagnosis remains uncertain despite testing and empiric treatment 3, 1
• Patient has experienced anaphylaxis requiring identification of specific triggers 3, 2