In scratch testing, what does a larger wheal indicate?

In scratch testing, a larger wheal typically indicates a more significant allergic response. When an allergen is introduced to the skin, an individual who is sensitized to that allergen will react with localized swelling and redness, known as a wheal. The size of this wheal correlates with the level of sensitivity to the allergen.

A larger wheal means that the immune system is responding more robustly to the allergen, suggesting a greater degree of allergy. This reaction is primarily mediated by IgE antibodies, which bind to mast cells and trigger the release of histamine and other chemicals causing the localized swelling.

In contrast, a smaller wheal would indicate a lower sensitivity or possibly even a negative response, meaning no significant allergic reaction occurred. While infections or normal responses may also cause skin reactions, they do not fit the context of wheal formation in the specific mechanism of scratch testing for allergies. Additionally, the presence of a large wheal itself is generally considered conclusive enough in many cases, thereby reducing the immediate need for further testing unless necessitated by clinical concerns.