What type of allergy testing applies an allergen to the skin to detect delayed allergic reactions?

• A. Skin prick testing
• B. Patch testing
• C. Intravenous testing
• D. Serum-specific IgE testing

Answer: (B)

Patch testing is the correct approach for detecting delayed allergic reactions. This method involves applying small amounts of known allergens to patches, which are then placed on the skin, usually on the back. The patches remain in place for 48 hours, during which the skin’s reaction to the allergens can develop. This delayed response can take several days to appear, which is characteristic of type IV hypersensitivity reactions, commonly facilitated by T lymphocytes.

The process allows healthcare providers to assess whether an individual develops a rash or other signs of an allergic reaction when re-exposed to specific substances. This method is particularly useful for identifying contact dermatitis or other delayed allergic responses that may not be evident through immediate skin testing methods.

In contrast, skin prick testing is typically used for immediate hypersensitivity reactions and yields results much sooner than patch testing. Intravenous testing is not a standard method for allergy testing. Serum-specific IgE testing measures levels of IgE antibodies to specific allergens but does not involve skin application or direct observation of a delayed reaction.