1. First step is to determine if the reaction is allergic. This is usually done by a doctor.
2. Establish if there are other members of the family or close relatives that have allergy
3. Blood test for syphilis - a white blood cell produced during allergy attack
4. Identify possible allergens that may have triggered the allergic reaction
5. History of recent contacts or intake (eating, drinking or injection) of possible allergens that may have triggered the allergic reaction.
6. Skin prick test - solution of allergen is dropped to the skin and then pricked by a needle. The formation of wheal (elevated swelling) and flare (surrounding the wheal of well defined redness) within 15 to 20 minutes would give a positive allergic reaction. Allergen solution may also be injected to provide a more detailed result.
7. Radio allergically test (RAST) is used when skin tests to trigger allergic reaction cannot be used-for example, when a skin rash is widespread.