Diagnosis & Specialist Care of Allergy & Clinical Immunology - Since 1982
About Specific IgE Blood Testing
Specific IgE blood testing is a widely used and trusted method for diagnosing allergies. It’s suitable for individuals of all ages and provides valuable insights into how the immune system responds to specific allergens. The test is sometimes referred to as RAST testing (although this is now outdated).
How Does Specific IgE Blood Testing Work?
This test measures the concentration of IgE antibodies in your blood in response to particular allergens. When your body encounters an allergen, IgE antibodies play a key role in triggering an allergic reaction. These antibodies stimulate mast cells to release histamine, leading to common allergic symptoms like itching, sneezing, and swelling.
Understanding IgE-Mediated Allergies
Allergies occur when the immune system overreacts to normally harmless substances, such as pollen, dust mites, or certain foods. IgE-mediated allergies are the most common type and typically cause symptoms within seconds or minutes of exposure. Non-IgE mediated allergies also exist, but they are less common and involve different immune responses with delayed symptoms. Specific IgE blood testing only detects IgE-mediated allergies, making it effective for identifying the most prevalent allergic reactions.
What the Test Results Mean
While a specific IgE blood test can indicate sensitisation to an allergen, it doesn't confirm an allergy on its own. High levels of IgE antibodies suggest that your immune system may overreact to a particular allergen, but the presence of these antibodies alone isn’t enough to diagnose an allergy.
To make a definitive diagnosis, your doctor will interpret the test results alongside your clinical history. Results are typically reported in grades which reflect how sensitised your body may be to an allergen:​
Grade 0
<0.35 KUA/L
Negative
Grade 3
3.5-17.5 KUA/L
Positive
Grade 6
>100 KUA/L
Strong Positive
Grade 1
0.35-0.7 KUA/L
Weak Positive
Grade 4
17.5-52.5 KUA/L
Strong Positive
Grade 2
0.7-3.5 KUA/L
Positive
Grade 5
52.5-100 KUA/L
Strong Positive
These grades help clinicians understand the level of sensitisation, but they must be carefully interpreted. A high sensitisation (grade 5 or 6) does not mean a more serious reaction is likely and conversely, anaphylaxis cannot be ruled out because the sensitisation level is low.
How Is the Test Performed?
A blood sample is required for specific IgE testing. This sample can be collected in two ways:
-
Venous Blood Draw:
Healthcare professional will draw blood using a needle.
-
Fingerprick Blood Sample:
In some cases, a capillary blood sample can be taken by pricking the finger.
Testing Capabilities
Specific IgE blood tests can target a single allergen or assess multiple allergens simultaneously. One of the most comprehensive tests available is the ALEX2 (Allergen Explorer) test, which can detect sensitivities to 295 different allergens, covering a wide array of food and environmental allergens.
