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Best Allergy Tests: Understanding the Options for Your Child
When it comes to diagnosing allergies, two primary testing methods are available: skin prick testing and blood testing. Parents often ask which is "better," but the answer isn't straightforward. Each method has distinct advantages in different situations, and at LACK Clinic, we often find that the tests complement each other, providing a more complete picture of your child's allergic profile.
The basics: How each test works
Before comparing the tests, it helps to understand how each one identifies allergies.
Skin prick testing
Skin prick testing works by introducing a tiny amount of allergen extract directly into the skin's surface layer. Here's the process:
- A drop of allergen extract is placed on the skin (usually the forearm or back)
- A small lancet gently pricks the skin through the drop
- If your child is sensitised to the allergen, a small, raised, itchy bump (wheal) will develop within 15-20 minutes
- The size of this reaction is measured and compared to control substances
Skin testing provides immediate results during your appointment and allows for testing multiple allergens simultaneously.
Blood testing
Blood tests for allergies (specific IgE testing) measure the amount of allergen-specific IgE antibodies in your child's blood. The process involves:
- A single blood sample is drawn
- The sample is sent to a laboratory for analysis
- Results typically take several days to become available
- The concentration of specific IgE antibodies to each allergen is measured
Modern blood tests can detect even very small amounts of these antibodies, providing a quantitative measurement of sensitisation to various allergens.
When skin testing has the advantage
Skin prick testing offers several benefits in specific situations:
Immediate results
Results are available within minutes, allowing your allergist to discuss findings and recommendations during the same appointment. This immediate feedback is particularly valuable when quick diagnosis is needed to guide urgent treatment decisions, when you've travelled a significant distance to get an allergy test in London, or when multiple potential allergens need to be ruled in or out efficiently.
Higher sensitivity for environmental allergens
Skin testing may be more sensitive for detecting allergies to:
- Environmental allergens like pollens, dust mites, and animal dander
- Respiratory allergens that may not show up as clearly in blood tests
- Seasonal allergens during peak exposure periods
Ability to test with fresh foods
When commercial allergen extracts don't contain all the relevant proteins (as is the case with some fruits and vegetables), skin testing can be performed using the fresh food itself, a technique called prick-to-prick testing. This approach is particularly valuable for:
- Diagnosing oral allergy syndrome
- Testing for fruit and vegetable allergies where commercial extracts may be inadequate
- Comparing reactions to raw versus cooked versions of foods
- Detecting allergies to foods where fresh testing proves more sensitive than standard extracts
Visual demonstration for parents
The visible reaction provides a tangible demonstration of your child's allergy, which some parents find helpful for understanding the condition. Seeing the reaction develop can make the abstract concept of allergy more concrete.
When blood testing has the advantage
Blood testing is particularly valuable in several scenarios:
Skin conditions that complicate skin testing
Blood testing is often the preferred option when:
- Your child has widespread eczema leaving insufficient clear skin for testing
- Dermographism is present (a condition where the skin reacts with welts to any scratch or pressure)
- Persistent hives (urticaria) would make interpreting skin test results difficult
Medication use that could affect results
If your child is taking medications that suppress skin reactions, blood testing provides more reliable results. These medications include:
- Antihistamines (even those taken several days before testing)
- Some antidepressants with antihistamine properties
- Long-term oral corticosteroids
Testing for severe allergies
For children with history of severe or anaphylactic reactions, blood testing may be preferred because:
- It eliminates any risk of triggering an allergic reaction during testing
- It can be less frightening for children who've experienced severe reactions
- It provides quantitative results that may help assess the severity of sensitisation
Young or anxious children
Some children, particularly those who are very young or anxious about medical procedures, may tolerate a single blood draw better than multiple skin pricks. In these cases, blood testing allows comprehensive assessment of multiple allergens from a single sample.
Monitoring changes over time
Blood testing provides precise quantitative measurements that are particularly useful for:
- Tracking changes in allergen-specific IgE levels over time
- Monitoring the potential resolution of allergies
- Assessing the impact of interventions like immunotherapy
When both tests are valuable
In many cases, combining both testing methods provides the most comprehensive assessment. This complementary approach is particularly useful for:
Resolving discrepancies
Sometimes a child's clinical history suggests an allergy that isn't confirmed by initial testing. Using both methods can help resolve these discrepancies and avoid missing clinically relevant allergies.
Comprehensive evaluation of complex cases
Children with multiple allergic conditions or atypical presentations often benefit from the complementary information provided by both testing methods.
Monitoring the evolution of allergies
Tracking both skin test reactions and specific IgE levels over time provides a more complete picture of how allergies are evolving. Decreases in both measurements more confidently suggest that an allergy may be resolving.
Component-resolved diagnosis
In some cases, especially for foods like peanuts and tree nuts, component testing (testing for specific proteins within an allergen) via blood tests can complement skin testing to provide more detailed risk assessment.
Understanding test limitations
Both testing methods have limitations parents should understand:
False positives
Both tests detect sensitisation (the presence of specific IgE antibodies) but cannot definitively diagnose clinical allergy on their own. Many children test positive to foods they can actually tolerate without reactions. This is why test results must always be interpreted alongside clinical history by an experienced allergist.
False negatives
No test is 100% sensitive, and both may occasionally fail to detect an allergy that is clinically present. This is more common with certain allergies, such as:
- Some fruit and vegetable allergies
- Certain drug allergies
- Contact allergies (which require patch testing rather than standard skin prick or blood testing)
Age-related considerations
Very young infants may have false negative results because their immune systems are still developing. Repeated testing may be necessary as they grow.
The role of clinical history
Regardless of which testing method is used, the most important factor in accurate diagnosis is the clinical history – the detailed information about your child's symptoms, their timing, and their relationship to potential triggers. This information guides:
- Which tests to perform
- How to interpret test results
- What recommendations to make based on these results
An experienced allergist integrates test results with clinical history to distinguish between true allergy and sensitisation without clinical relevance.
What to expect during testing at LACK Clinic
Before your appointment
Preparation depends on which test will be performed:
For skin testing:
- Certain medications, particularly antihistamines, may need to be stopped several days before testing
- Continue to give asthma medications and most other prescribed medications
- Feed your child normally before the appointment
For blood testing:
- No special preparation is required
- All medications can be continued
- Regular feeding schedules can be maintained
During the appointment
Our team will:
- Review your child's medical history in detail
- Explain the testing process appropriate for your child
- Perform the tests with techniques specifically adapted to minimise distress
- Interpret results in the context of your child's symptoms and history
- Develop a personalised management plan based on the findings
After testing
Following your appointment, you'll receive:
- Clear explanation of test results and their significance
- Written management plan for identified allergies
- Guidance on avoidance strategies if needed
- Prescriptions for appropriate medications
- Instructions for emergency treatment if severe allergies are confirmed
- Plan for follow-up and monitoring
Making the decision
The choice between skin testing, blood testing, or both depends on multiple factors specific to your child's situation. At LACK Clinic, we consider:
- Your child's age and ability to cooperate with testing
- Presence of skin conditions or medications that might affect results
- Severity of past reactions
- Number and types of allergens being assessed
- Urgency of obtaining results
- Your child's preference (for older children)
We take time to explain the reasoning behind our recommendations and involve parents in the decision-making process.
Our comprehensive approach to allergy testing
Rather than viewing skin testing and blood testing as competing options, we see them as complementary tools in the allergist's toolkit. Each has specific strengths that make it valuable in different clinical situations.
The "best" test is the one that provides the most reliable information for your child's specific circumstances, interpreted by an experienced allergist in the context of their clinical history. Sometimes this will be skin testing, sometimes blood testing, and often a combination of both.
At LACK Clinic, we tailor our approach to each child's unique needs, ensuring that testing is not only accurate but also as comfortable as possible, providing the information necessary to develop effective management strategies for your child's allergic condition.
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