How do you actually find out if you are allergic to something?
Unfortunately I’ve seen quite a few people turn to Dr Google to diagnose themselves with allergies to all sorts of things. Or pay large amounts of money for dodgy and unproven allergy testing. In the case of food allergy, this can lead to people avoiding whole food groups for no reason at all.
So what are genuine types of allergy testing? Which allergy tests are reliable and used by allergy specialists?
Our family has quite a lot of experience with the main types of allergy testing. For food and environmental allergies, this includes blood tests, skin prick testing and oral food challenges. And for drug allergies we’ve experienced intradermal (under the skin) testing. So we can share some personal insights on what it is like to have these tests done.
Difference between allergies and intolerances
Before we look at these tests in a bit more detail, keep in mind that these are tests for “IgE mediated” allergies, not intolerances.
An allergy is an immune system response. Your body reacts to something that it shouldn’t, as though it is harmful. And it happens reasonably quickly after you have been exposed to something you are allergic to. This could be immediately or possibly a couple of hours later. Allergies can cause mild to moderate symptoms or can lead to a severe reaction (anaphylaxis) which can be life threatening.
Intolerances on the other hand are normally a digestive response to foods. A problem breaking down certain foods or sensitivity to particular food chemicals. They can make you feel terrible, but are won’t cause a life threatening reaction. To get to the bottom of your food intolerances, you may need to consult a qualified dietitian. A dietitian can guide you through the process of elimination and reintroduction of particular foods.
Why have allergy testing?
The main reason to ask for allergy testing is of course when you suspect you have an allergy. Usually because you have experienced symptoms of an allergic reaction. This could be to food, insects or medicine or to something in the environment like grass pollen or dust mites.
Allergy testing can identify what triggered your reaction so that you can avoid it happening again. It can also help decide on appropriate treatment for managing your symptoms.
Symptoms of a mild or moderate reaction include:
- swelling of lips, face or eyes
- hives or welts
- tingling mouth
- vomiting or abdominal pain (*this can be a sign of a severe reaction to insect stings)
A severe reaction might start with moderate symptoms and get worse. Or it may come on suddenly. Any one of the following symptoms of a severe reaction requires urgent medical care:
- difficult or noisy breathing
- swollen tongue
- swelling/tightness in throat
- wheezing or persistent coughing
- difficulty talking or hoarse voice
- persistent dizziness or collapse
- pale and floppy (young children)
This is a medical emergency and you should use an Epipen if available and call an ambulance.
You night also have environmental allergies that cause different symptoms. Signs of these allergies are itchy eyes, a runny nose, sneezing, nasal congestion or itchy skin. Often this is allergic rhinitis (hay fever) caused by grass pollen. But you could also be allergic to house dust mites, animal dander or saliva or mould. These types of allergies are less likely to cause a severe reaction but can make life very unpleasant. And they can be treated, so there is a good reason to get tested.
Environmental allergies can also trigger asthma.
How to arrange allergy testing
The best person to see if you suspect you have allergies is an allergy specialist. In Australia you will need a referral from your doctor.
Your doctor might order some preliminary tests (such as blood tests), but an allergy specialist usually the best person to interpret any test results.
If you have already had a severe reaction to something and have been to hospital, the hospital may organise a follow up appointment for allergy testing for you.
Unfortunately we have a very high demand for allergy specialists in Australia and you may have to wait a long time for your appointment.
Your allergist will discuss your allergy symptoms with you to determine what the likely triggers are. Based on this, they will recommend the types of tests you should have and what allergies you should be tested for.
Most of our family has had a least one blood test, sometimes referred to as a RAST test. (RAST stands for “radioallergosorbent test”, a method which used to be used by the lab). You might also have heard of this as ImmunoCAP testing.
Generally blood tests are considered less sensitive than skin tests, but they can be very helpful. They can be a good initial screening test. Blood tests are sometimes used where the person being tested is unable to stop taking medication like antihistamines or steroids (which can affect skin testing). It might also be a good option for someone with eczema where skin prick testing is difficult. Some food allergens have particular proteins that are more allergenic. A blood test can test for antibodies to that protein (for example, araH2 testing for peanut allergies).
Blood test results also form part of a picture. Used together with skin prick tests and your symptom history, blood tests can help to decide if your allergies are improving or if a challenge test is an option.
What does a blood test involve?
Blood tests for allergies involve measuring the level of IgE antibodies your body produces in response to particular foods or things in the environment. Like other blood tests, the person taking your blood sample will use a small needle into the vein (usually on the inside of your elbow) to take a tiny amount of blood. Then the sample is send to the lab for analysis. You don’t need to stop taking antihistamines before having these tests, which can be handy if you suffer with bad allergy symptoms.
What do the results mean?
Interpreting the results of blood tests is not something you should try and do yourself.
Labs report test results in different ways. This might be as a measurement of the level of IgE antibodies (in kU/L), on a scale of 1 to 6, or even just as “absent”, “low”, “moderate” or “high”. Generally speaking, the higher the result the more likely you are to be allergic to the substance you were tested for. However, it isn’t that simple. You may be sensitised to something and not truly allergic to it. And different allergies have different thresholds at which specialists consider you to be at risk of having a more serious reaction. Importantly, a specialist will also interpret your results based on your own history of symptoms.
As an example, my RAST result for grass mix is over 6 kU/L, which is regarded as high, and I definitely suffer from very bad hay fever. So it is very likely I have a grass allergy. I haven’t yet been to see an allergist for skin testing and to talk about immunotherapy, but it’s on my to do list.
A negative blood test (no or very low antibodies) means that you probably don’t have an allergy.
(RAST/IgE blood tests are a form of genuine allergy testing. You may also have heard of IgG blood tests, which refer to a different type of antibody in the blood. These are not proven allergy tests, as discussed more below.)
The advantages of skin prick tests are that they are quick and convenient. The results are known straight away and you can discuss them with your specialist at the appointment.
What does a skin test involve?
Skin prick testing is where your allergist places a drop of an allergen extract on your skin and then pricks it with a tiny needle. This allows the the solution to go through the skin. Usually testing is done on the arm or back (particularly for children).
The first step is to clean the area and write numbers corresponding with the different things being tested. Secondly, drops of the allergen solutions are placed next to the numbers and lightly pricked. Two extra test spots are done as controls: one with histamine and one with saline. The histamine should produce a reaction and the saline drop should not.
After a set time (usually 10 minutes), the tester will measure any reaction. A “wheal” is a raised, sometimes itchy lump in the middle. The ‘flare’ is any spreading redness around the wheal. Your test results will include the measurements of both the wheal and flare in mm.
Skin prick testing can be a bit uncomfortable. Especially if you have a lot of positive results. I won’t lie, my son hates it. He has been having annual testing for many years now and he has multiple allergies. He has even sometimes broken out in hives from the allergen extracts. However the process is quite quick. You can wash the area and take an antihistamine straight away to sort out any itching and redness.
If your younger child is having tests, I highly recommend that you take something fun to distract them while you are waiting for the measurements. They need to sit still and not touch the extracts (which is why children often have the testing done on their backs).
What do the results mean?
A skin prick test is positive if the wheal measurement is 3mm or more, and negative if it is smaller than this. Sometimes the wheal and flare can be very large. We’ve had a wheal of 23 and a flare of 40 for pistachios, and a similar size for house dust mites.
Like with blood tests, your allergist will interpret the positive skin prick testing and the size of the wheal and flare. Just because you have a positive test does not mean that you are allergic. It can just indicate that you are “sensitised” to a particular substance. We’ve had a small “positive” skin prick test for wheat before, when our child was eating and tolerating wheat every day without any issues. Similarly, just because you have a very large positive result doesn’t mean that you are at risk of severe reactions. This is why your symptom history is such an important part of the picture.
Other types of skin tests
If you are being testing for a drug allergy or an insect allergy, you might have a different sort of skin test called “intradermal” testing. Here the tester will inject a small amount of allergen under the surface of the skin. I’ve watched this process to test for antibiotic allergies. Again, the size of the reaction indicates whether the test is positive or negative.
Patch testing is another type of skin test. This can be helpful to test for contact dermatitis reactions to things like metals or plants. A patch with the suspected allergen(s) is applied to the skin and left for a longer period (48 hours) to see whether it causes a skin reaction.
Oral food challenges (or antibiotic challenges) are really the ultimate test. The best way to know if you are allergic something is to actually eat it and see if you have a reaction.
We’ve been through a few of these now. Four oral food challenges and one antibiotic challenge so far. Some have been successful (milk in baked goods and one type of penicillin) and others haven’t been (I’m looking at you, cow’s milk and peanuts).
What does an oral challenge involve?
Unless your specialist has told you otherwise, and has given you very clear instructions, oral food challenges should be done under medical supervision. We have always had challenges done as an inpatient at our local hospital. Sometimes challenges can be done in the specialist’s office, but there should always be appropriate emergency medical care available in case you have a serious reaction.
In our experience, food challenges start with a very small amount of the food to see if there is any sign of a reaction. The dose amount increases at regular intervals until the person being tested has had a whole serve. With cow’s milk, we started with 5ml and worked up to a glass. For milk in baked goods, it was muffins. And for peanuts, it was a tiny amount of peanut butter (and stopped right there!).
For a drug allergy test, you doctor might give you the first dose of the medicine in the office and monitor for a time. You then continue to take a full course of the medicine at home.
What do the results mean?
A food challenge is successful if a whole serve is consumed without a reaction. In the event of a reaction, the challenge stops immediately and appropriate treatment given. Even if you have eaten a whole serve, you should continue to be monitored. Reactions can sometimes take a little later than you expect. We thought the milk challenge was a “pass” at first because we got to the end without a reaction. But about 20 minutes after the last dose, my then toddler had quite a serious reaction. It was fine, we were in the right place and the wonderful allergy clinic staff sorted it out very quickly. But that’s why you shouldn’t try oral food challenges at home.
If you have a successful food challenge, your treating doctor will explain to you what to do next. This includes how to introduce the food to your diet and ensure that you continue to eat it regularly.
On the other hand, if you do have a reaction to the challenge food, then your allergy is confirmed. Your allergist will talk to you about continuing to avoid the food. You may need to change your allergy action plan depending on the extent of your reaction, for example if you are advised to carry an EpiPen. If you are prescribed an EpiPen, you should read our comprehensive guide: Making Friends with your EpiPen
Unproven allergy testing
Unfortunately there are an increasing number of people offering testing for allergies that just doesn’t work. You may have seen these advertised online. Or offered by alternative medicine providers.
Even worse, some claim to be able to “cure” allergies.
They can also be very expensive.
Some of the unproven tests to avoid are:
- ALCAT tests
- hair analysis
- IgG antibody tests, which often claim to be able to test for hundreds of different allergies and intolerances from a single blood test
- vega testing
These tests are not genuine allergy testing. They are not scientifically proven and are not supported by Medicare rebates in Australia. You can read more about unproven allergy testing in the fact sheet produced by the Australian Society of Clinical Immunology and Allergy here: https://www.allergy.org.au/patients/allergy-testing/unorthodox-testing-and-treatment
Have you had any allergy tests done or taken your child for testing? Let us know how it went in the comments.