How is nut allergy diagnosed?

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Medical history and examination

Your doctor may suspect that you have a nut allergy from your symptoms. Your doctor may then ask a lot of questions. For example, the amount and type of food that you ate which caused a reaction, how quickly the symptoms started, how severe they were, how long they lasted, etc.

Skin prick test

This can help to confirm the allergy. A drop of nut extract solution is placed on your skin, usually on your forearm. Then, a needle prick is made through the drop. This is usually painless as just the very surface of your skin is pricked. However, it is enough to let a tiny amount of solution into your skin. If a reaction occurs, it happens within 20-30 minutes.

A positive reaction is when the skin under the solution becomes red and itchy. A white, raised swelling called a weal surrounds the red central area. A weal takes about 15-20 minutes to reach its full size, and then fades over a few hours.
A negative reaction is when the skin remains normal. This means that you are not allergic to the substance in the solution.

Do not take antihistamines on the day of the test as they may dampen any allergic response during the test.

Blood test

You may also have a blood test called a RAST test or an ELISA test. These measure the amount of a protein called IgE antibody which is produced as a result of an allergic reaction.

Food challenge

If, after a skin prick test and a blood test, the results still do not prove that you definitely have an allergy then your doctor may ask you to take part in a food challenge. You will be given foods to eat that may or may not contain nuts. You will then be watched closely for 15-30 minutes to see whether you have a reaction. Food challenges are always done at a hospital because of the risk of a reaction.

Once an allergy has been confirmed an allergy specialist will usually help you to devise a plan to manage it. This plan will be individual to you and will take into account how severe your reaction is.