Questions to Assist Understanding of Allergy Tests
a) Can I use the allergy panels to test delayed food allergies in children?
The immune system of an infant may not fully develop until 18-36 months of age and therefore the clinical relevance of IgG and ALCAT diagnostic testing in young infants is unknown. We recommend that IgG allergy testing is only performed for infants greater than 18 months of age. ALCAT testing may be useful in infants greater than 4.5 kilogram in bodyweight. It should be kept in mind however, that the immune system in infants is not fully developed and therefore immune reactions (as indicated by the ALCAT results) may change with the development of the child (For discussions on this issue refer to the section entitled Food sensitivity testing in children).
b) Which test should I choose for allergy testing?
Based on the knowledge that adverse reactions to foods can be caused by a wide range of factors and involve many parts of the body, it is understandable that diagnostic tests for food reactions may not test all possible causes. IgE food allergy testing should be used for the assessment of immediate food allergies (generally associated with anaphylactic reactions), whilst IgG food allergy tests analyse delayed food allergies, and ALCAT panels can analyse delayed food allergies as well as reactions to foods that involve histamine release, cytokine release and/or degranulation of leucocytes.
c) What is the difference between an IgG & IgE allergy?
The IgE mediated food allergy is well known, easily diagnosed and usually results in physical symptoms within minutes. The existence and classification of IgG food allergies have been more controversial. The IgG food reactions are difficult to diagnose (without a test) because the time between consumption of the offending food and the physical response may be delayed; even up to 3 days later. The symptoms are also often subtle. In many cases ingestion of the offending food paradoxically masks the symptoms temporarily.
d) What is an anaphylactic food reaction?
An anaphylactic food reaction is an immediate, severe and often life-threatening reaction to a food. This is mediated by an IgE immune response as set out in c) above
e) Do I have to eat foods I believe I have a reaction to, prior to having the test?
For the Food IgG Allergy Panels, you must include as many of the foods that are being tested in the two weeks prior to specimen collection. If foods are not included in the diet during this time false negative results may be obtained, as recent exposure to these foods may be required for antibodies to be present in the blood. Foods however that have caused an anaphylaxis reaction in the past should never be reintroduced into the diet without the specific guidance of an allergy specialist. For the ALCAT test you do not have to eat any specific foods prior to testing
f) How long do I have to be off my anti-histamine before I collect my specimen for the allergy tests?
We suggest that for the IgG and IgE allergy tests you avoid using anti-histamines, anti-inflammatories and any other immunosuppressive medications for two weeks prior to testing. For the ALCAT tests we will provide you with avoidance suggestions. Never discontinue prescription medications without first consulting your doctor.
g) The ALCAT or IgG Food Allergy results say that I do not react to a type of food that I once had an anaphylactic or severe reaction to. Should I start eating this food again?
If you have had an anaphylactic or severe reaction to a food it is likely that it is caused by an IgE mediated immune response. The ALCAT and IgG Allergy tests do not test IgE immune reactions; they only identify delayed responses to food. Therefore do not introduce a food into your diet that is suspected of causing an anaphylactic reaction, even if it is negative on the ALCAT or IgG Allergy test results.