How is urticaria diagnosed?

Diagnosis largely depends on examination of the skin where the typical appearance of weals with associated flaring and blanching confirm the condition. The cause may be established by taking a careful history of the mode of onset, the relationship to any potential trigger-factor, familial tendency or recent illness.

An allergic reaction may be confirmed by routine allergy tests such as skin prick test or the radioallergosorbent (RAST) test. However in many cases no specific cause is found.

Chronic urticaria is rarely due to allergy and routine allergy tests are of little value. Tests may be needed to exclude specific triggers or other systemic diseases that could give a similar reaction such as endocrine disorders, malignancies or systemic lupus disease.

Urticaria is also a known symptom of infestation with worms, such as strongyloides or filaria and this should be considered as a cause in patients with onset of urticaria following travel to areas where these organisms are endemic.