What are the differences between Skin Prick Test (SPT), ImmunoCAP and Immuno Solid-phase Allergen Chip (ISAC) tests for various allergic diseases and conditions?

From the Guidelines

Skin Prick Testing (SPT) is the most commonly used first-line test for diagnosing allergies, while ImmunoCAP and ISAC are used in specific situations, such as when SPT cannot be performed or for complex cases requiring immunotherapy. The choice of test depends on various factors, including the patient's medical history, skin conditions, and the need for precise measurements of specific IgE antibodies.

Key differences between SPT, ImmunoCAP, and ISAC tests:

• SPT is a quick and inexpensive test that involves applying allergen extracts to the skin surface, but it requires patients to stop antihistamines before testing and carries a small risk of systemic reactions 1.
• ImmunoCAP is a blood test that quantitatively measures specific IgE antibodies to individual allergens, providing more precise measurements than SPT, but it's more expensive and results take longer 1.
• ISAC is a multiplex assay that simultaneously measures IgE antibodies against 112 molecular allergen components from 51 allergen sources, helping to identify specific molecular allergens causing reactions and distinguish between primary sensitization and cross-reactivity 1.

Advantages and applications of each test:

• SPT is the preferred test for diagnosing IgE-mediated sensitivity, but it may not be suitable for patients with severe dermatitis or those who cannot discontinue antihistamines 1.
• ImmunoCAP is particularly useful when SPT cannot be performed, and it provides more precise measurements of specific IgE antibodies, but it's more expensive and results take longer 1.
• ISAC is especially valuable for patients with complex allergies or those requiring immunotherapy, as it helps to identify specific molecular allergens causing reactions and distinguish between primary sensitization and cross-reactivity, but it's the most expensive option and is typically reserved for complex cases after initial testing with SPT or ImmunoCAP 1.

Clinical considerations:

• A careful history is the most important step toward the diagnosis of allergic disease, and skin testing or in vitro tests for specific IgE antibodies should be used to confirm or exclude suspected causes of the patient's symptoms 1.
• The number of skin tests performed may vary depending on the age, potential allergen exposures, and area of the country, and it's essential to know which aeroallergens are present locally, are clinically important, and have cross-reactivity with botanically related species to interpret skin tests or in vitro tests for specific IgE properly 1.

From the Research

Differences between SPT, ImmunoCAP, and ISAC tests

• The Skin Prick Test (SPT) is a commonly performed, inexpensive test that gives immediate results, while ImmunoCAP is a laboratory test that measures serum allergen-specific IgE antibodies 2.
• ISAC (Immuno-Solid Phase Allergen Chip) is a multiplex assay that enables testing for specific IgE against multiple allergen components 2, 3.
• In patients with nut allergy, ImmunoCAP had a higher detection rate (71%) compared to SPT (56%) and ISAC (65%) 2.
• For oral allergy syndrome, ISAC had a higher detection rate (88%) compared to ImmunoCAP (69%) and SPT (33%) 2.
• ImmunoCAP was more effective in detecting wheat allergy, with a 100% detection rate, compared to ISAC (67%) 2.

Comparison of SPT and ImmunoCAP

• A study comparing SPT and ImmunoCAP for diagnosing house-dust mite allergy found that SPT was more useful for subjects under 50 years old, while ImmunoCAP was more useful for subjects over 50 years old 4.
• Another study found that ImmunoCAP had a higher agreement with SPT (63.9-93.2%) compared to immunoblotting assay (68.4-86.2%) for allergen detection 5.

Clinical Applications

• The choice of test depends on the specific allergic disease or condition being diagnosed, with ImmunoCAP being preferred for nut, wheat, and food allergies, and ISAC being preferred for oral allergy syndrome 2, 3.
• SPT is recommended as the first choice for patients under 30 years old, while ImmunoCAP is recommended for patients over 50 years old 4.
• Non-invasive and minimally invasive techniques, such as dried blood samples, may provide a cost-effective and well-tolerated alternative for primary or home care sampling 6.