Auckland DHB Clinical Immunology and Allergy
Public Service, Allergy and Immunology
Food Allergy Testing and Diagnosis
Testing for food allergy
The diagnosis of food allergy has become much more common in the last 20 years. It was rare before the 1980s, now about 15% of the population report that they have a food allergy. Is this increase in perceived food allergy due to:
- an increase in real food allergy for some reason?
- an increase in testing for food allergy so we just pick it up more?
- or more widespread use of inaccurate food allergy testing and diagnosis?
There is some evidence to support all three of these factors.
This is very unfortunate, because there are significant social and psychological effects of having a label of food allergy.
Did you know?
- In studies where the population is asked in surveys whether they have a food allergy, 15% report that they do. In some studies where allergy is accurately diagnosed with a "blinded" food challenge, it turns out only 2% are allergic. This means that many people are labouring under a false diagnosis and experiencing the social and psychological burden of an incorrect and unnecessary food allergy diagnosis.
- Alternatively, genuine food allergy can cause anaphylaxis (a serious allergy reaction) and be dangerous (although actual fatalities are extremely rare). Furthermore, admissions for anaphylaxis have doubled in the last ten years and a study from Melbourne using food challenges found a positive rate of 10% of the population.
These are 2 reasons why accurate diagnosis of food allergy is essential.
It's important to know if you do have it, it's important to know if you don't have it...so how do we find out?
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.
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 of 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.
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, 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 before allergy tests are ordered.
Common food allergies
Over 90% of food allergies are caused by:
- Milk allergy
- Egg Allergy
- Peanut allergy
- Tree nut allergy (Cashew, Pistachio, Almond, Walnut, Hazelnut, Brazil Nut, Pecan)
- Soy allergy
- Wheat allergy
- Fish allergy
- Shellfish allergy.
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 tree nuts.
It is exceptionally rare to have new onset milk or egg allergy as an adult.
Sometimes wheat can be associated with exercise induced urticaria/hives or anaphylaxis in adults.
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, tree nut 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® ?
For those with food allergy, an Epipen® 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® (Adrenalin Auto-injector)
Will I die 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 1 in 50000. Alternatively, US statistics say the lifetime risk of dying in a car is 1 in 80 (more than ten times higher). Therefore if you have a peanut allergy, you should be more afraid of the car ride to the restaurant, than the chance of dying from peanuts hidden in the meal. This does not mean we should be complacent about taking appropriate precautions, and eating out is one of the main times anaphylaxis from hidden peanut ingredients can occur, but it is reassuring for patients with peanut allergy who can be constantly fearful for their lives.