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Food Allergy

Food Allergy Panels (IgG and IgA)

The following article on Food Allergy Testing (IgG and IgA Panels : Blood Spot and Serum Tests) is from the Rocky Mountain Labs web site.www.rmalab.com.

Allergy IgG - IgA

Allergy Testing - Blood Spot Test

Two of the antibodies involved in allergic reactions are immunoglobulin E (IgA) and immunoglobulin G (IgG). IgA production occurs right after ingestion or inhalation of an allergen and is referred to as a Type I immediate hypersensitivity reaction. IgG antibodies are produced for several hours or days after exposure to an allergen and are called Type III delayed hypersensitivity reactions.

There are several subclasses of IgG, with IgG1 and IgG4 of primary interest. IgG1 is believed to be the main inflammatory component as IgG4 does not activate the complement pathway. Nevertheless, IgG4 induces histamine release, and is a contributor to delayed sensitivity reactions. The IgG Allergy-Blood Spot Test measures Total IgG (includes subclasses 1,2,3,4).

IgG Delayed Onset Allergies

In a Type III delayed hypersensitivity reaction, IgG forms an immune complex with the allergen/antigen (Ag), which activates the complement pathway and releases inflammatory mediators wherever the immune complex is deposited. This process takes anywhere from several hours to several days, which is why hypersensitivity reactions are delayed. Although macrophages pick up the IgG-Ag complexes immediately, they have a finite capacity to do so. If there are a lot of antigens present, the macrophages may saturate their capacity to remove the immune complexes, causing the excess to be deposited in tissue. Depending on which tissues are involved, deposition of these IgG-Ag complexes may result in the following health concerns:

  • Vascular deposition: headaches, vasculitis or hypertension
  • Respiratory tissue deposition: alveolitis, asthma and recurrent infections
  • Skin deposition: dermatologic conditions
  • Joint deposition: joint pain
  • Rhinitis and angioedema may occur as a result of histamine release by immune complexes

IgG allergies are difficult to diagnose because reactions do not occur until hours or days after ingestion of an allergen. This makes it extremely difficult to determine which foods are the causative agents. Blood spot testing for IgG provides a simple and practical means for practitioners to uncover potential causes of allergic reactions and allergy related disease. For detailed information on sample collection, go to the Test Specification Sheet.

Validity

IgG testing via blood spot is just as accurate as IgG testing via serum, and has the advantage of requiring only a small amount of blood. Rocky Mountain Analytical compared data obtained via blood spot and serum and found results to be virtually identical. Information regarding reasons for unexpected negative or positive results follows:

False Negatives: If the allergen was not consumed anytime in the 3 weeks prior to testing, the immune system may not have had recent enough exposure for IgG antibodies to be present. The form of allergen being tested is not the same as what the patient reacts to. For example, whey protein is altered by high heat, so someone with a whey allergy may have no reaction to heat-altered milk products. Food intolerances may mimic the symptoms of a food allergy but are not the result of an immune reaction. For example, lactose intolerance is due to a deficiency of lactase, the enzyme responsible for the digestion of lactose. Adverse reactions to food additives may also be defined as food intolerance. Another type of adverse food reaction is psychosomatic food aversion, which can result from a previous negative food experience (e.g. food poisoning).

False Positives: False positives may occur as a result of cross-reactivity with other foods or proteins. The proteins are not identical, but similar enough that the immune system reacts to them. For example, a reaction to bananas may also cause a reaction to pineapple and vice versa.

IgG Test Reports

IgG reactions develop slowly, up to several hours or days after exposure to a food allergen, so testing is often the only way of determining which foods are responsible. The allergy test report graphs IgG immune response to each of the tested food allergens. Reactions are categorized as no, low, moderate or high.

Leaky Gut Syndrome

An overload of antibody-allergen complexes can cause inflammation in the lining of the gut, and this inflammation causes the gut to ”leak‘. The leaky gut then allows more antibody-allergen complexes to escape into tissues, which provokes more food allergies. Therefore, anyone with leaky gut should be tested for food allergies and anyone with significant food allergies may need to be treated for leaky gut.

Medication Use

Concomitant antihistamine use for allergy symptoms is acceptable as the test measures immune response, not histamine levels. However, IgG-IgA allergy testing is not useful for people on immunosuppressant drugs like prednisone, chloroquine or azothioprine.

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