Allergy

In a skin prick test, a drop of an allergen solution is first placed on the skin. The spot is then pricked gently with a sterile lancet to introduce the allergen into the top layer of the skin. A similar procedure is done with salt water as a negative control and a chemical called histamine as a positive control.

If there is a skin reaction, such as an itchy raised surface area (wheal) or a surrounding redness (flare), after 15 minutes (compared to the salt water control), this suggests that the person is allergic to the substance in question.

Intradermal skin tests are commonly used in the diagnosis of drug allergies. In this test, a small amount of allergen is injected into the skin. This form of testing is more sensitive than an SPT and can produce more frequent adverse reactions.

Allergy blood tests are used to diagnose allergic conditions by measuring specific antibodies in the blood. Here are some common types of allergy blood tests:

1. RAST (Radioallergosorbent Test): This test measures the total amount of IgE antibodies in the blood, which can be elevated in individuals with allergies. Specific IgE tests can also be performed to identify the exact allergens causing the allergic reactions.
2. Allergen Component Testing: This advanced form of allergy testing goes beyond identifying specific allergens. It breaks down the allergens into their individual allergen components to pinpoint which specific parts within an allergen the patient is reacting to. This is particularly useful for complex allergens like peanuts, where different proteins can cause varying degrees of reactions.
3. Basophil Activation Test (BAT): This test measures the activation of basophils (a type of white blood cell) when exposed to allergens. BAT can be useful for diagnosing drug allergies, food allergies and other complex allergic conditions.

A patch test is a procedure used for diagnosis of allergic contact dermatitis, as small amounts of various potential allergens, i.e. substances that might cause an allergic reaction, are applied to the skin for 48 to 72 hours using adhesive patches. With evaluation by allergists, it helps determine whether a specific substance causes inflammation after contact with skin. Common contact allergens include metals such as nickel, gold and silver, fragrances and perfumes, cosmetics and latex.

A patch test is different from a skin prick test; the latter checks for immediate allergic reactions caused by pollen or food.

Dermoscopy is a non-invasive diagnostic tool that offers enhanced visualisation and assessment of allergic skin conditions. Its applications include diagnosing contact dermatitis, monitoring eczematous dermatitis, evaluating urticarial and insect bite-related allergic reactions and assessing drug reactions. Dermoscopy also helps our allergists make informed decisions with detailed insights into skin changes.

A drug challenge is performed to exclude or confirm allergy to a drug. It involves introducing gradually increasing amounts of the suspect drug by oral, inhaled or other routes. Given the risk of severe allergic reactions, the test must be carried out in an appropriate setting by competent staff and only if clinically indicated.

In oral food challenges, patients are first given a small amount of suspect food. They will then gradually receive increasing doses over time under close medical supervision. As the gold standard for diagnosis of food allergies and related disorders, oral food challenges can confirm or rule out food allergies. It can also help determine one’s tolerance level to an allergen for safe consumption and advanced treatment planning.

This test is carried out to evaluate airway hyperreactivity, which is a hallmark of asthma. Methacholine is a synthetic choline ester that acts as a bronchoconstrictor to narrow the airways. The test is particularly sensitive for diagnosing asthma in individuals who exhibit symptoms suggestive of asthma despite normal lung function tests.