Explore Allergy Testing: Skin Prick Testing vs. Blood Tests
Author: Dr. Libby Forbes · Last Updated: July 2026
Comprehensive Guide to Allergy Testing
Diagnosing food and environmental allergies often begins with a detailed clinical history. When history alone is not definitive, allergy testing helps clarify potential allergens. The two primary methods are skin prick testing and allergy blood tests.
Can Allergy Testing Alone Diagnose Allergies?
Neither skin prick testing nor allergy blood tests can independently confirm an allergy with absolute certainty. Both may produce false positives or false negatives. The definitive diagnosis of a food allergy often remains a supervised oral food challenge. All results must be interpreted alongside clinical history.
Can Allergy Testing Predict Severity of Reactions?
No. Current testing identifies likelihood of sensitisation but does not reliably quantify how severe a reaction may be if exposure occurs.
Skin Prick Testing (SPT)
What Is Skin Prick Testing?
SPT is a frontline diagnostic method typically performed on the forearm. Allergen extracts are placed on the skin and the outer layer is gently pricked. A sensitised patient may develop a localised wheal response.
How Are Skin Prick Test Results Interpreted?
After 15 - 20 minutes, sites are examined. A positive reaction presents as a raised itchy wheal. Controls ensure validity:
- Positive control (histamine): should elicit a response
- Negative control (saline): should not evoke a reaction
Preparing for Skin Prick Testing
- Avoid oral antihistamines for at least three days prior
- Manage eczema affecting the testing area
- Continue other prescribed medications unless advised otherwise
Possible Side Effects
Localised itching, redness or swelling is common and usually resolves within one to two hours. Systemic reactions are extremely uncommon in supervised settings.
Allergy Blood Tests
What Are Allergy Blood Tests?
Often referred to as ImmunoCAP (or historically RAST), these measure allergen-specific IgE antibodies in the bloodstream, indicating sensitisation that must be correlated with symptoms.
When Are Blood Tests Preferred?
When skin testing is contraindicated (severe eczema, widespread skin conditions), when antihistamines cannot be stopped, or when SPT results are inconclusive.
How Are Allergy Blood Tests Performed?
A standard blood draw at a pathology collection centre. No special preparation is required. Results are generally available within one to two weeks.
Interpreting Allergy Blood Test Results
False positives and negatives are possible. Relevance is evaluated considering IgE level, the allergen tested, and clinical history.
Learn more
For more detailed information visit ASCIA (allergy.org.au). Paedix offers specialised allergy and immunology services - learn more at Allergy & Immunology Services.