Allergy Testing

Targeted Blood Testing for Suspected Allergy

An allergy occurs when the immune system reacts to a substance that would normally be harmless. Depending on the allergen and individual response, symptoms can include itching, hives, swelling, nasal symptoms, wheezing, gastrointestinal symptoms or, in severe cases, anaphylaxis.

YT Medical offers blood testing for selected suspected allergies using allergen-specific IgE testing. Testing should be guided by the patient’s symptoms and history rather than screening indiscriminately against large numbers of unrelated substances.

A positive result demonstrates sensitisation to an allergen, but it does not automatically prove that exposure to that substance is responsible for a patient’s symptoms. Results need to be considered alongside what actually happens when the suspected allergen is encountered.

Which Allergy Blood Tests Are Available?

Blood testing can measure Specific Immunoglobulin E (specific IgE) directed against selected allergens. Depending on the patient’s history and the laboratory tests available, this may include individual or grouped allergens relating to areas such as:

• Foods, including selected nuts, milk, egg, wheat, fish or shellfish.
• Pollens, including grass, tree and weed pollens.
• House dust mites.
• Animal dander, such as cat or dog allergens.
• Moulds and other environmental allergens.

Where appropriate, more detailed component-resolved testing may also be available for certain allergens. Rather than measuring IgE against an entire allergen extract, component testing looks at individual allergenic proteins and can sometimes provide additional information in more complex allergy assessment.

The exact allergens selected should reflect the patient’s history rather than simply ordering the largest panel available.

Specific IgE and Total IgE

Specific IgE measures antibodies directed against a particular allergen and is the more relevant blood test where a defined allergy is being investigated.

Total IgE measures the overall amount of IgE circulating within the bloodstream. Levels can be raised in people with allergic conditions, but also in several other circumstances, meaning Total IgE cannot diagnose a particular allergy on its own.

A normal Total IgE does not necessarily exclude allergy, and an elevated result does not identify what somebody is allergic to.

Food Allergy Is Different From Food Intolerance

Food allergy and food intolerance are not the same condition. A true food allergy involves an immune response, while food intolerance can result from difficulties digesting or processing particular foods and does not generally carry the same risk of anaphylaxis.

Commercial food-specific IgG or broad “food intolerance” blood panels should not be interpreted as equivalent to clinically validated IgE allergy testing. Unselective testing can produce results that lead people to remove multiple foods unnecessarily without establishing that those foods are causing symptoms.

Where gastrointestinal symptoms rather than immediate allergic reactions are the principal concern, another diagnostic pathway may be more appropriate.

When Might Allergy Blood Testing Be Useful?

Specific IgE testing may be helpful where the symptoms and timing suggest an immediate-type allergic reaction and there is a reasonable suspected trigger. Blood testing can also be particularly useful where skin-prick testing is impractical or where antihistamine medication makes skin testing more difficult.

However, complex allergy, previous anaphylaxis, suspected drug allergy or uncertainty about a significant reaction may require assessment through a specialist Allergy service rather than blood testing alone.

A severe allergic reaction causing breathing difficulties, significant swelling, collapse or other features of anaphylaxis requires emergency medical treatment.

Understanding Your Results

Specific IgE results need to be interpreted together with the clinical history. A person can have detectable IgE to a substance without developing symptoms when exposed to it, a phenomenon known as sensitisation.

For this reason, patients should not make major dietary restrictions or assume that a positive laboratory result establishes a clinically important allergy without appropriate interpretation.