Diagnosing allergy involves carefully considering the history of how a reaction came about and what could have caused it. This is generally done by asking a series of questions relating to the reaction but also regarding general wellbeing, diet, details of any other illnesses, and medications/ inhalers/ ointments.
Following this, skin prick tests thought most appropriate to the allergy may be done. Allergy tests can support the clinical impression, but should not be used for screening as they may lead to false positive reactions and result in children avoiding food unnecessarily.
Sometimes after skin prick testing a further step called an open challenge is done to confirm the diagnosis. For some a blood test may be done instead of skin prick testing.
Your specialist will provide you with suggestions on avoidance and treatment based on the test results.
It is a type of allergy test. A drop of the suspected substance causing your reaction is placed on the skin.
In some instances the test is done using the juice from fresh fruit or using cooked food. This is called prick-to-prick testing. Your specialist will let you know if they need to do this test. They may ask you to bring the food to the clinic for the test. If more than one food is to be tested then you should bring the food in separate sealed containers like small Tupperware boxes or sandwich bags to keep the foods from touching each other and contaminating the test.
The skin is pricked with the solution with what looks like a mini plastic pencil. The skin is then wiped. It takes only 15 minutes to get the result.
The test itself involves a series of pricks and although this can be slightly uncomfortable there are no needles! The test is usually done on the forearm. If the forearms are affected by eczema then the test can be done on the back or on the thigh.
Skin prick testing takes 15 minutes, the entire consultation can last from 30-45 minutes.
All tests have their limitations. Allergy tests are not screening tests to be used when the cause is unknown. They are most useful if done when there is a good history of a reaction and the result will support the clinical diagnosis. Where there is doubt a challenge to the food may be organised in hospital by your doctor.
Skin prick tests are best avoided in patients with widespread eczema or those taking antihistamines or steroid tablets. Sometimes blood testing will be done as an alternative.
Skin prick tests are safe tests which will at the most cause minor local irritation to the tested area. This settles on its own in 30-45 minutes. Washing the area under running water can be helpful.
After the test you can go about enjoying your day as planned.
Yes, you can help in 3 ways:
- Think about what happened when the reaction occurred. Your doctor will want to know the details of what happened when you got your reaction. Thinking through and if possible writing down the sequence of events leading to the reaction will be useful. It can be helpful to ask others (friends, teachers, dinner lady) who were also there what they saw. Photos or videos are sometimes really helpful.
- Bring a list of foods or other possible allergens that could have caused the reaction. It is helpful for the doctor to know what you could have reacted to. Foods eaten within two hours of the reaction are likely to be the cause. An empty packet of suspect foods or getting the chef’s list of ingredients used in the recipe can be helpful.
- Remembering to bring all medicines/ inhalers.
The specialist will appreciate you bringing current prescriptions.
The skin prick test result is affected by the use of antihistamines or steroid tablets. If you are able to, then the antihistamines should be stopped at least FIVE days before your appointment.