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Diagnosing allergies and intolerance

Diagnosing allergies and intolerance

With so many options available to test for allergies nowadays, how would the average Joe know which test is the most accurate? Dietitian Katrina Pace investigates.

Around one in five people in New Zealand and Australia has an allergy. It’s one of the fastest growing public health issues in the country.

With the increases in allergies and food intolerances there’s been a boom in over-the-counter tests that may (or may not) tell you what you’re having a reaction to. So, what tests can you trust to tell you if you have an allergy or intolerance?

Most common allergens

  • Dust mites
  • Cats
  • Dogs
  • Pollen
  • Food (cows’ milk, peanuts, tree nuts, soy, gluten, dairy, eggs, seafood and fish are the most common)
  • Drugs
  • Mould
  • Latex

What is an allergy?

An allergic reaction happens when the body overreacts to a trigger it sees as harmful to the body. It releases immunoglobulin E (IgE) antibodies in response to the trigger, which we call an allergen.

The symptoms experienced when you have an allergic reaction are the IgE antibodies causing chemicals to be released. Sneezing, a running nose and excess mucous production are all ways the body hopes to flush the allergen from your system. Inflammation can also occur as part of the immune reaction. Your nose, eyes or throat may start to swell. Stomach upsets and pain, gastrointestinal bleeding and skin problems (eczema, urticaria and itching) may also be symptoms of allergic reactions.

While most allergic reactions are mild or moderate, not causing major problems, some people can experience a life-threatening symptom called anaphylaxis where the immune reaction causes tissues to swell, potentially narrowing airways.

Breathing may become difficult or ,in some cases, impossible. An injection of adrenaline (such as from an Epipen) reduces the swelling and increases blood flow through the veins, allowing breathing to become normal again.

Histamine is a chemical that the immune system produces when provoked by an allergen. That’s why the most common medications given to reduce the effect of an allergic reaction are antihistamines.

Antihistamines come in the form of tablets, liquids or nasal sprays. Corticosteroids may also help to calm the immune reaction and are available in nasal sprays or topical creams. Saline rinses or eye drops can help to remove the trigger allergen and are a non-medicated way to reduce the allergic reaction.

Other than allergies, there are other types of reactions caused by the immune system being triggered inappropriately. Two of the most common examples of this are coeliac disease and food protein-induced enterocolitis syndrome (FPIES).

Allergy or intolerance?

If the reaction doesn’t trigger a response by the immune system it’s called a sensitivity, adverse reaction or intolerance.

Common causes of adverse reactions are microbial contamination or toxins, reactions to additives, enzyme deficiencies (e.g. lactase deficiency causing lactose intolerance), psychological or neurological reactions or a group of conditions called ‘inborn errors of metabolism’.

How can I tell whether it’s an allergy or not?

As a true allergy causes an IgE-mediated immune reaction, the main way to tell whether you’re suffering with an allergy or an adverse reaction is to test for an immune response to a trigger. Sarah Elliot, dietitian at Food Savvy, says, “We occasionally have people ask if we offer food allergy/intolerance testing. These are popular as they give what (people) feel to be certainty and clarification. A useful initial conversation to have is the difference between an allergy and intolerance, as it can be, understandably, confusing.”

Skin prick test

The Australasian Society of Clinical Immunology and Allergy (ASCIA) recommend skin prick testing (SPT) as the primary method for diagnosing IgE-mediated allergies. This is generally well tolerated and has the least risk of serious side effects. A few drops of a liquid containing the allergen is put on the skin of your forearm or back, then a prick is made through the liquid, so a small amount of it goes under the skin. A positive test is the appearance of a red, itchy lump on the skin within 15–20 minutes, where the skin prick was made. The result is measured in millimetres. Generally, a measurement of 3mm or greater indicates a positive reaction.

A SPT can give information on what specific allergens you may be reacting to but needs to be carefully interpreted. It’s also useful to note that the size of the SPT reaction doesn’t match the severity of your allergic symptoms, it just indicates an allergy or not. Also, a positive SPT can occur without symptoms, as it may be a ‘clinically silent sensitisation’ or ‘clinical false positive’. It’s also important to note that the SPT doesn’t test for non-IgE-mediated allergies, sensitivities or intolerances. SPT should only be carried out by trained medical and paramedical professionals with access to treatments for anaphylaxis.

Intradermal testing (IDT) is another type of skin testing for allergies

IDT, or scratch testing, is used for testing an allergic reaction to drugs or insect venom. Generally, it’s not used to test for allergies to dust mites, pollen or food. It’s not as reliable as SPT and is more uncomfortable.

Allergen-specific IgE blood test (RAST test)

If SPT is not available, then allergen-specific IgE blood tests may be used to diagnose allergies. Other reasons to use a blood test may be when the skin is affected by the allergen (severe eczema) or when medication may affect the accuracy of the results of the SPT.

Oral allergen challenge test

For testing food or medication allergies an oral challenge may be requested. This may help determine if allergy symptoms have reduced over time or if the cause of a reaction hasn’t been confirmed by other tests. These tests are usually only done by a medical professional with access to resuscitation facilities.

Even with positive skin prick tests and blood tests the interpretation of results can be complicated, which is why it is safest to be assessed by a trained, specialist medical professional.

Other tests

If you ask Dr Google (or Siri) about what allergy tests you should get, a whole other range of tests will come up — but just how reliable are they?

In 2012 the New Zealand Commerce Commission stated, “The Commission’s view is that allergies can only be diagnosed on the basis of clinical history and symptoms, confirmed, if necessary, by either a skin prick test, blood test or oral food challenge — all of which should only be performed by an appropriately qualified medical practitioner.”

Ms Elliot from Food Savvy reports that she’s seen a few clients who have had microbiome testing. “Our understanding of the gut microbiome and what that means to how we eat is still (in the) very early days,” she says.

Hair test

Currently hair testing for allergies and intolerances is one of the most popular tests. And while testing a snippet of your hair to see if your symptoms are caused by an allergy may seem a painless option, there’s no science behind this.

Tests for an allergic reaction depend on being able to assess whether an IgE-mediated reaction has occurred in response to a trigger. As there is no IgE in hair, testing it can’t give a measure of an allergic reaction. Hair tests are not recognised by any medical allergy specialists and research does not back up the use of hair testing for assessing allergies.

Electrodermal testing, eg VEGA test

Electrodermal testing involves holding one electrode in your hand while another electrode is put on an acupuncture point elsewhere on the body. Glass vials containing the suspected allergen are then placed in the circuit and the changes in electrical current are monitored. There are no studies investigating whether this technique can accurately and reliably establish allergies to food triggers. Two studies have looked at reliability for diagnosing airborne allergens, and both showed that electrodermal testing was neither accurate nor reliable.

Kinesiology

Using kinesiology to diagnose food allergies can be popular as it doesn’t require anything other than to hold a bottle containing the allergen while the therapist applies downward pressure to the subject’s arm.

A weakness in the arm, in theory, indicates a sensitivity to the trigger in the bottle. A review concluded that there was no evidence to support kinesiology for any diagnosis.

IgG food testing

IgG is another immune marker, like IgE. If IgE tests are negative, then IgG tests may be suggested to identify a food sensitivity rather than allergy. A recent review of unproven diagnostic tests for adverse reactions to food reports that IgG antibody production is a normal immune function, and that developing IgG antibodies has been linked to food desensitisation and tolerance, rather than the opposite that it is claimed to identify. The position of the American Academy of Allergy, Asthma and Immunology is that food-specific IgG reactions do not indicate food allergy or sensitivity.

Seeking help for other allergies or sensitivities?

Your first port of call, if you suspect you’re suffering from symptoms of a food allergy, is your family doctor. From there they can make a first-line assessment, recommend initial tests and get you referred to a specialist if needed. You may be referred to a specialist in allergies, clinical immunology or gastroenterology, depending on your symptoms or the results of clinically-proven tests.

If you bypass them and go straight to a naturopath or postal allergy-diagnosis testing centre, you risk misdiagnosis as well as missing other causes of your symptoms.

Other conditions that may masquerade as a food allergy include:

  • Coeliac disease
  • Dermatitis herpetiformis
  • Inflammatory bowel diseases
  • Bowel cancer
  • Autoimmune disorders
  • Stress

Getting a wrong diagnosis may mean that you’re cutting out foods you may not be reacting to, making lifestyle choices you don’t need to and even missing treatment of a potentially life-threatening condition.

Cutting out gluten or dairy, for example, means you’re at more risk of missing out on essential nutrients, such as B vitamins, calcium and fibre, and switching to a free-from diet is often more expensive. Initial improvement in symptoms may be the result of just paying more attention to your diet, choosing more whole food and less processed foods and the placebo effect.

What tests to ask for to check for food intolerances

Coeliac tests

A blood test can check whether your symptoms could be caused by coeliac disease, an autoimmune condition causing the body to mount an immune response to gluten. Typically, coeliac disease has gastrointestinal symptoms, such as diarrhoea, but it may also cause bloating, pain and symptoms similar to other food intolerances. Dermatitis herpetiformis is a type of coeliac disease where the symptoms are itching, blistering skin rashes. If coeliac disease is indicated after blood testing this is followed up with a biopsy which is the gold standard for diagnosis. It’s worth remembering that going on a gluten-free diet before being diagnosed with coeliac disease will interfere with getting a correct diagnosis, giving false negatives or unreliable answers.

Hydrogen breath test

The hydrogen breath test can be used in the diagnosis of a FODMAP intolerance, specifically lactose, fructose and sorbitol malabsorption.

Exclusion and challenge tests

For many food intolerances the primary diagnostic tool is a period of exclusion followed by a strict food challenge procedure. This needs to be done under the guidance of a trained and experienced professional to make sure the testing process and results are as accurate as possible.

Food allergies and gut health in the news (2019)

There are differences in the gut bacteria of children with cows’ milk protein allergies and those without. Intestinal bacteria may be important in regulating our response to food allergen triggers to allergic diseases. Could modifying our gut bacteria help prevent cow’s milk protein allergy? We don’t know the answer yet.

Another study has found distinct differences in the gut bacteria of people with food allergies, leading to consideration that gut microbiota profiles may be used in diagnosis.

Similar gut microbiota differences were found in children with asthma and allergic rhinitis, indicating that gut bacteria could also play a role in non-food allergies.

Allergies and weaning your baby

ASCIA describe an infant with severe eczema, or a sibling or parent with allergies, as having a high risk of developing a food allergy. Infants with severe eczema and/or egg allergy are at increased risk of developing an allergy to peanuts. Feeding these infants peanut foods before the age of 12 months significantly reduces the risk of developing peanut allergy.

At around six months old, but not before four months, start introducing infants to solid, iron-rich foods. Give infants common allergen foods (peanut, tree nut, cow’s milk, egg, wheat, soy, sesame, fish and shellfish) including smooth peanut butter/ paste, cooked egg, dairy and wheat products before the age of 12 months, unless they’ve already been diagnosed with an allergy to that food. This is recommended for all infants, including those with severe eczema. Remember, whole nuts and seeds are a choking risk for children under five, so use smooth nut and seed butters to introduce nuts and seeds.

Excluding foods during pregnancy or breastfeeding is not recommended, unless an allergy has been clinically diagnosed. When introducing foods, give them regularly (twice a week) as part of a varied diet, to maintain tolerance. Trying a food and then not giving it again may result in food allergy development.
If you suspect a food allergy, stop giving that food and seek medical advice.

First published: Sep 2019

Article sources and references

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