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Allergy testing for children: An eczema parent’s guide

Child undergoing skin prick allergy testing. His sleeve is rolled back and his forearm has a grid drawn on it. And adult is dropping allergy solution into the squares with a pipette. He looks mildly concerned about the process.
Finding the trigger for their child’s eczema so that it can be avoided is the holy grail for eczema parents. Not surprisingly, allergy testing is often seen as the way to achieve this. However, as with all things eczema – allergy testing in children is not as straight-forward as it sounds. We look at when and why allergy testing is used for eczema kids (and when it’s not). We also look at the different types of testing available and share our top tips for getting the most from your appointment with the allergy clinic.

If your child has a reaction and you suspect it’s an allergy, speak to your GP. They will ask you about your child’s symptoms and medical history and may refer your child for allergy testing. There are a number of different allergy tests available. The test used will vary depending on the age of your child, the type of allergy suspected (IgE or non-IgE), other conditions your child may have such as asthma, other medications and whether your child’s eczema is flaring at the time of testing.

When can my child get an allergy test?

One common frustration of eczema parents is that allergy testing is routinely not offered to younger children, especially those under 5 years old. This is because children’s immune systems are not fully developed. This means that differences in their IgE antibody levels (the markers used to identify allergies) are not as pronounced as those in older children and adults. This makes the test results harder to interrupt and less reliable.

In addition, both blood testing and skin testing can be distressing for young children. As a result, the usual advice for young children with manageable symptoms is to avoid the suspected allergen and treat with antihistamines and steroids/emollients as necessary. Children under 5 with moderate or severe eczema that isn’t responding to emollients and steroid creams may be offered allergy testing if it is not possible to identify triggers through observation. Of these, under 2s are usually offered a skin pick test as this is typically less distressing than taking blood.

Types of allergy test

Blood testing

Specific IgE tests (sometimes known as RAST – Radioallergosorbent tests) check blood for the IgE antibodies that trigger given allergic reactions. The specific antibodies tested for will usually be determined by the medical history taken by your doctor. For example, if a peanut allergy is suspected, they will test for peanut specific IgE in your child’s blood. If your child also suffer from allergic rhinitis, they will be tested for airborne allergies like house dust mites, pet dander and pollens. Results are not available immediately so you’ll need to separate appointments: one for the blood sample and one to talk through the results. You may also need an initial appointment for your doctor to determine which allergies to test for.

For children, blood samples are usually taken from the back of the hand. Typically the area is numbed first with an anaesthetic cream. This cream takes around 30 minutes to work and you may well have time to find the hospital café or go for a walk while it takes effect. The nurses will cover the cream with a dressing so it stays put. Take plenty of things to entertain your child as these blood tests can involve a lot of hanging around. There is no need to avoid antihistamines in the days before blood testing.

Skin prick or scratch testing

Like the blood tests, skin pick tests are measuring IgE antibodies. In this case in the skin rather than the blood. Skin prick testing is typically done on the forearm or back. It involves having a drop of test solution containing the suspected allergen applied directly to the skin. The tester will then use a small, hand-held needle to break the surface of the skin under the test sample. This is the pick or scratch and introduces the allergen into the surface of the skin.

It is common for more than one allergen to be tested at the same time, using separate areas. Expect to come away with reference numbers written on your child’s skin. A negative control (saline solution) and a positive control (histamine) are used to ensure the test is accurate. If there is a sensitivity to an allergen, a red wheal similar to nettle sting will form around the prick. The size of each wheal gives an indication of the level of sensitisation to each allergen. These welts will reach their maximum size in around 15-20 minutes and will usually fad within an hour.

It’s important to note that being sensitised to an allergen only means your child’s immune system has come into contact with that allergen previously and remembered it. It does not necessarily mean they are allergic to it. Avoiding a potential allergen that the body is sensitive to but has previously tolerated can results in a loss of tolerance. Test results must be considered in conjunction your child’s medical history and so require careful interpretation by the doctor.

Unlike with blood tests, antihistamines cannot be taken for at least 3 days before skin prick testing. However they can be used to manage any positive test results. If your child is suffering from an eczema flare this type of testing is not always appropriate. Your appointment may be rescheduled or you may be offered a different type of test. Your healthcare advisor will talk through this with you at the time of making the appointment. 

If an allergy is diagnosed during testing, your child may suffer a wider allergic reaction such as sniffles, watery eyes and skin rashes. These should subside over the next few days and can be managed with antihistamines. While anaphylactic reactions to allergy tests are extremely rare. However, these tests are only carried out in facilities that are able to deal with these events. You may be asked to stay at the clinic for a few hours following the tests, just in case there are any delayed reactions. Make sure you have plenty of entertainment for your little one with you.

Patch testing

This is the standard way of testing for non-IgE-mediated contact allergies (the ones that take longer to present). A patch test involves samples of suspected allergens (test solutions or suspected toiletries) held in small containers being tapped to the skin. These containers hold the allergens against the skin and are worn for 48 hours before being checked and reattached for another 48 hours. Irritated skin indicates a potential allergy. These tests typically take place over 1 week with appointments on Monday, Wednesday and Friday. As with other allergy tests, the results must be read by an expert.

Patch testing is not used for airborne or food allergies but typically covers around 40 common contact allergens including rubber, metal, fragrances and plants. It is not 100% accurate but is a good baseline to work from. The patches can be itchy and uncomfortable. It is also important that the patches stay in place for the duration of the testing. As a result, patch testing is not usually recommended for young children.

In order for patch testing to be accurate, you will need to avoid using steroid or calcineurin inhibitors creams on the area for at a week before testing starts. Your child may also need to stay out of the sun as tanned skin can also affect test results. Antihistamines shouldn’t affect the results. The patches are typically labelled by writing directly onto the skin so it’s sensible to use old clothing that you don’t mind getting ink on.

Boy facing away from the camera not wearing a top. He has two strips of allergy patch test containers being stuck to his back by a doctor with surgical tape.
Patch testing can be itchy and the patches need to stay in place and dry for 4 days. This, and the small size of a young child’s back, means that patch testing can be an impractical option.

Allergen provocation/challenge testing

This involves direct exposure to a potential food allergen – usually orally (swallowing) or by injection. It is known as provocation/challenge testing as it is designed to provoke symptoms as confirmation of an allergy. 

This type of testing will be done in a clinic as an outpatient appointment and may take several hours. During this time your child will be constantly under medical supervision, you will need to remain in the clinic for at least an hour after the final test is administered. Anti-histamines cannot be taken for a few days prior to testing as they will undermine the results. 

As the aim of this type of testing to provoke an allergic reaction these tests are done very carefully, especially in young children. It is likely only a tiny amount of the test substance will be given initially and then slowly increased if necessary. The idea is to diagnose or confirm the continued existence of an allergy as quickly as possible with minimum reaction and discomfort. There is always the risk of a severe reaction or anaphylaxis with this type of testing which is why it is important that it is carried out by medical professionals in a clinical setting where they have the means to quickly counter such a reaction. With food allergies, the food used to in the test will probably be well-cooked as this reduces the likelihood of a serious allergic reaction.

You will be asked to sign a parental/guardian consent form and then basic observations will be taken – blood pressure, pulse and peak flow (breathing) reading. Only one allergen is introduced at a time. After the introduction of the potential allergen your child will be closely observed for allergic reaction. 

Elimination diets

Food allergies may be diagnosed with a trial elimination diet. This is where the suspected food is removed from your child’s diet for two to six weeks before being reintroduced. Their symptoms will be monitored throughout. Elimination diets should only be conducted with medical supervision to ensure that you child is not missing out on vital nutrients. For example iodine, found in eggs and dairy products, is important in children’s brain development.

A word about commercial at-home allergy tests

There are several tests available online or in shops which offer tests that can be done at home. These include hair analysis and muscle testing. They are inexpensive but they are not scientifically proven. Use of these tests is strongly discouraged by the NHS as they can be very misleading.

Preparing for an allergy child’s test

  • Check whether you need to pause any of your child’s medication. This information should be included in your appointment details. You may also need to keep your child out of the sun for the few days running up to their appointment. Some medications need to be paused a week before testing. Also check whether you should not use emollients on your child’s back / arms on the day of the appointment.
  • Check your appointment letter to see what the clinic would like you to bring to the appointment. This might include your child’s red book, medication and creams, food/symptom diaries, things that you know cause reactions (like toiletries, food packaging, googles or jewelry) or photographs of visible symptoms like rashes.
  • If your child is old enough, take time to explain what is likely to happen. Tests can be scary and a bit uncomfortable, especially if you don’t understand what is going on. There are lots of great resources available you can look at with them. There’s a great, child-friendly video about skin prick testing here. 
  • Make sure your child has had something to eat before you arrive. This will help them not to feel woozy if they aren’t good with the sight of blood. (As well as avoiding them getting hangry if there are delays.)
  • Take plenty of entertainment, snacks and drinks with you. This is specially true if your appointment is at a ‘one-stop-shop’ allergy clinic. These appointments often last 2-3 hours and there can be a lot of waiting around.
  • If your child is still a baby it is a good idea to have a car seat, baby carrier or pushchair for them to fall asleep in if needed. Do check with the clinic first as some have limited space and prefer pushchairs to be left at the entrance. In which case a sling or baby carrier will save your back.
  • Note them down the things that you want to understand from the appointment and take you list with you. Some NHS clinics can be overwhelming and feel like you’re on a production line. If you have your questions noted down, you’ll be able to check that you’ve got all the answers you need when you’re asked: ‘any questions before you go?’.

As well as sharing our experience of bringing up an eczema child (and favourite allergy-friendly recipes), ScratchSleeves also manufacture and sell our unique stay-on scratch mitts and PJs. We now stock sizes from 0-adult in a range of colours. Visit our webshop for more information.

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Written by:

Tess joined ScratchSleeves in 2016 and loves being able to help our little clients and other parents who are struggling.

Reviewed by:

Coming from a family of eczema sufferers, Jae draws on years of practical, first hand experience living with eczema.

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