Auckland DHB Clinical Immunology and Allergy
Public Service, Allergy and Immunology
How to tell if you have a Food Allergy
Auckland Hospital Immunology Clinic Food Allergy Testing and Diagnosis
What are the usual symptoms of food allergy?
Most food allergy causes marked symptoms to come on within 90 minutes of eating the food.
The type of symptoms that occur include:
- urticaria or hives with food
- angioedema (swelling of lips, eyes or tongue) with food
- wheezing, coughing, difficulty breathing with food
- anaphylaxis (a severe reaction which can cause collapse)
- mouth itching after food
- marked sudden nausea and vomiting diarrhoea abdominal pain with specific food.
It is important to note that all these symptoms can be caused by things other than food. In fact 80% of cases of hives (urticaria) in adults are not due to an allergy, but rather due to other causes (which we can also investigate and treat.)
Other non-specific symptoms - Is it food allergy?
In general symptoms such as headache, tiredness, bloating, trembling, fatigue, constipation are very unlikely to be a food allergy.
Unfortunately often these nonspecific symptoms are diagnosed as a food allergy. Tests such as "hair analysis" or "IgG blood testing" make claims without proof with regard to such symptoms.
What is a food challenge?
One of the best tests to investigate this is a double blinded placebo controlled food challenge (DBPCFC).
With this test the patient is given either the food in question (disguised in a capsule, or something like yoghurt) or a placebo. Neither the patient nor the doctor knows if the patient is given a placebo or the food.
That way both the patient's and the doctor's preconceptions of what might happen are removed. This is in fact the "gold standard" test of food allergy. It should only be done in a monitored environment and in patients in whom the history of allergy and skin testing/blood tests do not suggest any significant risk.
In NZ self-reported rates of food allergy are up to 15%. In studies of food allergy done by double blind test, these are usually positive in only 2 - 5%. This means that about 10% of our population may believe they have a food allergy when, in fact, they don't.
This is quite problematic for them for two reasons:
- They have to avoid food and all the social issues with food avoidance can be significant
- The 'real' cause of their symptoms does not get diagnosed because it is put down to food allergy.
Unfortunately real food allergies also exist, and can cause alot of anxiety. A recent well conducted study of infants in Melbourne found rates of food allergy as high as 10%, and admissions for anaphylaxis (severe allergic reaction) have doubled in the last ten years.
So how do I find out if I have an allergy or not?
The only way to work out which of these situations applies to you, is to see a doctor:
- with a good knowledge of allergy
- who has experience in the use of the scientifically validated ways of testing for allergy
- who takes a detailed clinical history (essential)
- then uses only the appropriate skin tests and/or IgE blood tests.
After this a discussion must take place between doctor and patient about:
- has allergy been completely ruled out now?
- is allergy definitely confirmed now?
- is allergy still possible but not definite. In this case should a challenge test be considered?
What to do with this information is a decision made together, taking into account the information the immunologist provides, with the patient weighing up their options and deciding what to do. This can be an individual decision for each patient, according to what is important to them.