(Specific IgG testing to food antigens)
From the Philippine Society of Allergy, Asthma and Immunology
In recent times, allergists have been approached by patients who believe that their symptoms are related to a “food allergy.” Some medical practitioners and diagnostic centers have advised them to undergo serum IgG testing. Once these patients get their results with positive results to several food items, they then go to the allergists for interpretation of these results.
These patients have been reporting a variety of symptoms which are often attributed to food, either as a food allergy or food intolerance. These two medical conditions fall under the main medical diagnosis of an adverse food reaction.1 Oftentimes, patients mistakenly interchange these two medical terms when they relate their reactions to food. However, these two conditions are distinct medical entities. A food allergy is a reaction to a specific food allergen that elicits an immunologic response in predisposed individuals. The prevalence rate of food allergy is 8 percent in children and 5 percent in adults.2 However, the prevalence of perceived food allergies has been noted to be much higher.
A study done by Castor et al documented that in Filipino adults the prevalence of undocumented food allergy is 46 percent versus a prevalence of only 4 percent for true food allergy based on a validated questionnaire.3 An allergic response to a food antigen is initiated by Immnoglobulin E (IgE), an antibody, present in high levels in an allergic individual. The end-result of any allergic reaction is the release of histamine which causes systemic symptoms such as runny nose, sneezing, cough, eye redness and tearing, rashes, swelling of body areas (angioedema) and sometimes difficulty of breathing, low blood pressure and loss of consciousness (anaphylaxis).4
Thus, the detection of specific IgE to the suspected food allergen must be done to truly diagnose a food allergy. This is done through an allergy test that can either be a skin prick test or a serum specific IgE test. A positive food allergy test can have many false positive results and, thus, a positive food allergen test, in order to be accurate, must be correlated with consistent histamine-induced clinical reactions that occur upon ingestion of the specific food.
A negative test, however, can be highly predictive of the absence of a food allergy to the specific food antigen tested.5 Thus, a skin test more accurately tells one what he/she can eat rather than what the individual cannot eat. There are 8 food allergens that can most commonly trigger allergic reactions. These are eggs, milk, peanut, tree nuts, wheat, soy, fish and shellfish.
Food intolerances, on the other hand, occur due to abnormal physiologic responses to certain food. They are basically nonimmunologic, occurring due to metabolic problems such as enzymatic defects (i.e. lactose intolerance), pharmacologic (i.e. MSG reactions), toxic (i.e. food poisoning) and other undefined reactions. They are often mistaken as food allergies, but the mechanisms by which some food intolerances occur are not yet well defined. Since food intolerances are basically nonimmunologic, there is usually no involvement of any antibodies in these reactions. 5,6,7
Recently, alternative medicine practitioners have been diagnosing food intolerances using detection of serum IgG levels. Many non-specific symptoms attributed to food reactions to food antigens (i.e. gluten) are reported to be caused by elevated serum specific IgG in the individual. This practice may have come about in the early 1980s since one study showed that human IgG4 antibodies can cause basophil histamine release in vitro (8,9). However, mainstream medicine, does not support this concept.
Food allergen specific IgG or IgG4 antibodies are markers of natural exposure to food components, which are naturally recognized as foreign by the immune system. This situation is a normal beneficial immune reaction that does not lead to development of disease. Elevated IgG levels to food proteins can merely indicate that the individual has been exposed persistently to particular food antigens and has developed oral tolerance to these foods, rather than intolerance.8,9
Thus, measurement of food-specific IgG and IgG4 antibodies are not recommended for the diagnosis of food allergy or intolerance.1,2,10 Till the present, there are no validated diagnostic tests to prove or disprove food intolerance. Temporary elimination diets and food challenges may be helpful in diagnosing a food intolerance but these must be conducted by trained medical specialists in order to avoid inadvertent malnutrition in the patient.6
Specific IgG testing (food intolerance test) is NOT a diagnostic test for any allergic condition for the following reasons:
1. Elevated IgG levels, specifically IgG4, indicate tolerance to a particular food allergen.
2. Development of tolerance means that the patient will not react to a food antigen.
3. Allergic conditions, on the other hand, are caused by the action of IgE antibodies, not IgG antibodies, on the target organ. Allergic diseases, being IgE-mediated hypersensitivity reactions, can have an early phase and late phase component.
4. Therefore, only specific IgE testing is useful, together with a good clinical history and physical examination, in making a definitive diagnosis of any allergic condition.
Neither is specific IgG testing recognized as a test for the diagnosis of any food intolerance.
The Philippine Society of Allergy, Asthma and Immunology (PSAAI) does not support the practice of medical doctors or diagnostic centers that offer such tests given the evidence against the validity of such tests. The results may lead to unwanted consequences when incriminated foods that are well-tolerated by patients are removed from the diet. This can lead to clinical consequences such as nutritional deficiencies or even malnutrition. This can also lead to unnecessary expenses on the family of these patients because these tests are even more expensive than accepted allergy skin tests or serum specific IgE tests. The results of these IgG tests have serious consequences as compelling the individual to undergo expensive and complicated diets, or be prescribed unnecessary medications, which can lead to stress, anxiety and eventual depression. Well-tolerated foods, then, should not be removed from the diet even in the presence of positive IgG tests.
The PSAAI DOES NOT RECOMMEND the use of food-specific IgG testing for purposes of identifying or predicting adverse reactions to food.
1. Boyce JA, Assa’ad A, Burks WA, Jones SM, Sampson HA, Wood RA, et al. Guidelines for the diagnosis and management of food allergy in the United States: report of the NIAID-Sponsored Expert Panel. J Allergy Clin Immunol. 2010;126(suppl 1): 1105-1118.
2. Sampson HA, Aceves S, Bock SA, James J, Jones S, Lang D, Nadeau K, Nowak-Wegrzyn A, Oppenheimer J, Perry TT, et al. Food allergy: a practice parameter update-2014. J Allergy Clin Immunol. 2014;134(5):1016–1025.
3. Castor MR, Abong JM, de Leon JC, Alava HA, Kwong SL. Prevalence of food allergy among adult Filipinos using a validated food allergy questionnaire in the National Nutrition Health Survey (NNHeS) 2008. Philippine Journal of Allergy, Asthma and Immunology. July – Dec 2014; 17 (2): 18-32
4. Simons FE. Anaphylaxis. J Allergy Clin Immunol. 2010;125:161–181.
5. Wallace DV, Bahna SL, Goldstein S, Hamilton RG, Cohn JR. American Academy of Allergy, Asthma and Immunology Work Group Report: allergy diagnosis in clinical practice. J Allergy Clin Immunol. 2007;120: 967–9.
6. Brostoff, J., & Challacombe, S. (2002). Food Allergy and Intolerance (2nd ed.). Saunders Ltd.
7. Jones SM, Burks AW. “ The Spectrum of Allergic Reactions to Foods”. In: Food Allergy: Adverse Reactions To Foods And Food Additives. Dean Metcalfe et al. 5th ed. Oxford, UK: John Wiley & Sons, Ltd, 2014. 134-143. Print.
8. Hamilton, Roger. “In Vitro Diagnostics Methods In The Evaluation Of Food Hypersensitivity”. In: Food Allergy: Adverse Reactions To Foods And Food Additives. Dean Metcalfe et al. 5th ed. Oxford, UK: John Wiley & Sons, Ltd, 2014. 110-120.
9. Stapel SO, Asero R, Ballmer-Weber BK, et al. Testing for IgG4 against foods is not recommended as a diagnostic tool: EAACI Task Force Report. Allergy. 2008;63:793–6.
10. Muraro A, Werfel T, Hoffmann-Sommergruber K, Roberts G, Beyer K, Bindslev-Jensen C et al. EAACI food allergy and anaphylaxis guidelines: diagnosis and management of food allergy. Allergy 2014;69:1008–1025.
August 2017 Health and Lifestyle