Dr Andrew Baker Auckland Allergy Specialist Immunologist

Testing for food allergy

The diagnosis of food allergy has also become much more common in the last 20 years. 

Food allergy is much more common, and the reasons for this are still undergoing investigation.

Not everyone who has been labelled as allergic to a food, actually is, or perhaps the allergy may have gone away.  It is really helpful to get accurately tested, to then know what precautions you do have to take, and what precautions are no longer necessary.

Diagnosing food allergy -  symptoms of food allergy, skin tests, and blood tests

Investigating food allergy requires careful discussion of a patient's symptoms.  Simply ordering skin tests or blood tests alone is not sufficient.  These are useful diagnostic tests, but only when analysed together with a patient's symptoms because they are probability markers, so interpretation depends on the type of test, the level of positive result and the pre-test probability (as judged by your symptoms).  There is an extensive scientific literature to help guide the interpretation of these tests. 

Typical symptoms for food allergy should occur within about 90 minutes of eating, and include:

• hives urticaria after eating
• sudden itch of body or mouth with eating
• swelling lips tongue or eyes angioedema after eating
• lightheadedness with eating or collapse
• wheezing, coughing or difficulty breathing with eating
• sudden marked nausea, vomiting or diarrhoea after eating (usually with some of the above symptoms also)

If any of these symptoms occur within about 90 minutes of eating a specific food, a food allergy is possible.

For people who do not have symptoms of food allergy, then large panels of allergy testing with skin tests or allergy blood tests can be unreliable, and give incorrect diagnoses.  For this reason, accurate assessment by a doctor with good experience in allergy diagnosis is critical.  We can help look at all the possibilities for food related symptoms.

The gold standard for food allergy testing is a food challenge, which we also do at our clinic (but at a later date, not on your initial appointment).

There is no good quality scientific evidence to support "hair testing" for allergies, and numerous websites can be found on the internet offering non-evidence based IgG blood tests for allergy and large panels of unguided IgE testing which can also be unhelpful and misleading, so beware of that.

If you can't see an immunologist/allergist, then see your GP if you want to consider allergy testing.

Common food allergies

Some food allergens that can be an issue:

• Milk allergy
• Egg allergy
• Peanut allergy
• Treenut allergy (Cashew, Pistachio, Almond, Walnut, Hazelnut, Brazil Nut, Pecan)
• Soy and other legume allergy
• Wheat allergy
• Fish allergy
• Shellfish allergy.
• Sesame/tahini
• Wheat and exercise/co-factor allergy
• Alpha-gal allergy (delayed allergy to mammalian meat
• Buckwheat allergy
• Goats cheese

Which food allergies affect children?

All of these allergies can occur in children.  Milk and egg allergies in infants often resolve (but not always).

Which food allergies affect adults?

New onset allergies in adults are most often shellfish, fish, peanut, or treenuts.  

Also we see, buckwheat, wheat and exercise, alpha-gal, goats cheese, candlenut

It is rare to have new onset cows milk or egg allergy as an adult.

Sometimes wheat can be associated with exercise induced urticaria hives or anaphylaxis in adults and this can occur at rest too.

Some rarer and occasionally missed allergies (can be adult onset)

Wheat and exercise induced allergy

Buckwheat

Goats cheese / milk

Alpha-gal (delayed allergy several hours after eating to red meat or offal)

Candlenut

Treatment for food allergy

The first step is accurate diagnosis. Next, information must be provided about which foods need to be avoided.

Click this link for information on peanut, treenut and seed allergy

An action plan for allergy should be provided with a supply of antihistamines.

A discussion with your doctor should involve whether an adrenalin auto-injector such as an Epipen or Anapen is necessary.

Do I need an Epipen® or Anapen®?

For those with food allergy, an Epipen® or Anapen® is necessary if:

• there has been anaphylaxis (a severe allergic reaction which compromises breathing or blood pressure causing lightheadedness, weakness or fainting)
• there is asthma as well (this increases the chance of severe reaction).

Click this link for more information on Epipen® and Anapen® (Adrenalin Auto-injectors)

How big are the risks from food allergy like peanut allergy?

Dying from food allergy is very rare.  If you have a peanut allergy, one study estimated the yearly risk of dying from peanut allergy as one in 50000.  Alternatively, US statistics say the lifetime risk of dying from a car accident is one in 80, (more than ten times higher).  Therefore if you have a peanut allergy, you should be more afraid of a car ride than the chance of unknown peanuts in a meal.  This does not mean we should be complacent about taking appropriate precautions, including having an action plan with consideration of an adrenalin autoinjector eg epipen, as well as a clear avoidance plan, but it is also reassuring to know these risks are not that high for those with peanut allergy who sometimes can be constantly fearful for their lives day to day.