Diagnosing dermographic urticaria is relatively simple: a wooden spatula or capped pen is stroked across the skin (of the back) with moderate pressure. Almost all humans will demonstrate a skin reaction to this, known as dermographism (Greek for "writing on the skin"). For healthy patients, the mechanical stimulation causes a "red dermographism" that is no more than a brief reddening of the skin. This reaction is completely normal and expected for healthy skin.
Dermographism with dermographic urticaria is unmistakeably different. It consists of an extended area of red skin called a flare with an itchy, raised wheal within it. Dermographic urticaria is diagnosed if during testing:
- Itchiness sets in
- a flare arises that extends out beyond the trigger spot
- wheals form
- these skin manifestations diminish no later than several hours later without further consequence