Working out what caused your allergy begins with asking about what happened and what you were doing at the time. For instance, were you eating, sleeping, exercising? Had you taken any medicines? Had you had the food or medicine before?
Only some problems seen in the allergy clinic will require allergy testing. Allergy tests may be helpful in working out what caused an immediate allergic reaction after contact with a substance. They are usually not useful if there was a delay of more than a few hours before the reaction started. Thus, these tests are not usually helpful in working out what might be triggering flares in your eczema.
A challenge to the food or drug may be needed to confirm the diagnosis.
A drop of the substance suspected of causing the reaction is placed on the skin. The test is usually done on the forearm. The skin is pricked with what looks like a mini plastic pencil. The skin is then wiped. It takes only 15 minutes to get the result.
Sometimes the test is done using fresh fruit or cooked lentils. This is called prick-to-prick testing. Your specialist will let you know if they need to do this test, as you will have to bring the food to the clinic for the test. You should bring the foods in separate sealed containers like small Tupperware boxes or sandwich bags to keep them from touching each.
Skin prick testing takes 15 minutes, the entire consultation can last from 30-45 minutes.
The test involves a series of pricks. Although it can be slightly uncomfortable there are no needles!
All diagnostic tests have their limitations. A “positive” allergy test result does not necessarily mean that you will have an allergic reaction to the food, drug, pet, or pollen. The clinician in the allergy clinic will need to interpret the results in the context of your history. Where there is doubt a challenge may be organised in hospital.
Allergy tests are most useful if they back up a clear history of an immediate allergic reaction. A positive test result can support the clinical diagnosis.
Allergy tests should not be done as a fishing exercise, as where there is no clear trigger, the chances of them being right is usually less than 50%, or in other words less than just tossing a coin.
Skin prick tests should be 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. You may experience itching where the allergy solutions are put on the skin. Scratching can make the itching worse. The itch settles on its own within 30-45 minutes. Washing the area with water can be helpful. After the test, you can go about enjoying your day as planned.
Yes, you can help in three ways:
- Think about what happened when the reaction occurred. Your doctor will want to know what you were doing when you had the reaction. Think through and write down the sequence of events, including how long after exposure the reactions started. Ask friends, teachers, or the dinner lady who were there what they saw and what was in the food. Photos or videos can also be helpful.
- Bring a list of foods or other possible substances that could have caused the reaction. Foods eaten within an hour of the reaction are more likely to be the trigger. Bring empty food packaging or get the chef’s list of ingredients to your appointment.
- Remembering to bring all medicines/ inhalers.
Bring a list of current medicines to the appointment.
The skin prick test result is affected by antihistamines or steroid tablets. If you are able, then antihistamines should be stopped at least FIVE days before your appointment.