Dr Andrew Baker - Immunologist and Allergy Specialist - North Shore Auckland
Private Service, Allergy and Immunology, Internal Medicine
Food Allergy Testing and Diagnosis
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. 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 things.
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 studies where allergy is accurately diagnosed with a "blinded" food challenge, it turns out only 2-5% 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). Admissions to hospital for anaphylaxis have doubled in the last ten years, and a recent study in children in Melbourne found the rates of food allergy to be 10%.
These are 2 reasons why accurate diagnosis of food allergy is helpful. It can be helpful to you to know for sure if you are food allergic, and just as important to find out if you are not food allergic.
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 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, then 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.
Common food allergies
Over 90% of food allergies are caused by:
- Milk allergy
- Egg Allergy
- Peanut allergy
- Treenut 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 treenuts.
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, 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®?
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)
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 one in 50000. Alternatively, US statistics say the lifetime risk of dying in a car 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, but it is reassuring to know for those with peanut allergy who sometimes can be constantly fearful for their lives.