IgG, IgE, and Celiac Tests Prep


Instructions for Clinicians and Patients


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 — CLINICIANS — 

Medications May Impact Results

Certain medications may impact test results. Please note that the reference ranges were established based on patients taking no medications or supplements. In some instances it is unknown what potential impact a medication may have on test results. Genova never recommends that patients discontinue medically necessary medications or supplements in order to complete testing. There may be times when a patient may stay on a medication or dietary supplement during testing in order to evaluate its effectiveness. The recommendation to discontinue any substance is intended to establish a baseline finding. If you choose to discontinue a medication, a good rule of thumb is to take the biological half-life of the drug times 5 to allow for 'clearance' before testing. With certain medications, the drug itself may have cleared the body, but the effect of the medication may be longer lasting.

The following medications may influence the antibody test results; they would not be expected to interfere with the ability to run the assay itself:

  • glucocorticoids (e.g., oral prednisone, steroid metered-dose inhaler, cortisone cream)
  • chemotherapy
  • other immunosuppressive agents (e.g., Humira, Rituxan)
  • NSAIDS (e.g., Ibuprofen, Naproxen, Aspirin)
  • anticonvulsants (e.g., Carbamazepine, Valproate)

These medications can either increase or decrease immunoglobulin levels, and may result in false positive or false negative test results. Omalizumab is a monoclonal antibody designed to bind to free serum IgE, which may influence test results. Heparin interferes with the measurement of tissue transglutaminase (tTG) antibodies on the celiac panel.

The following medications DO NOT interfere with testing or influence biomarker levels: antibiotics, antihistamines, antidepressants. Antihistamines and antidepressants are known to interfere with skin prick testing, not blood testing for allergies.

Clinicians may use the allergen-specific IgE antibody test to monitor response to immunotherapy (desensitization).

Length of Exposure to Antigens

Important: If a patient has a known IgE-mediated food allergy, Genova DOES NOT recommend exposure to the food that may cause a reaction.

When testing for food antibodies, it is suggested that the patient eat a variety of foods for 2-3 weeks prior to testing (except for foods that are known to cause severe reactions). Doing so will help to ensure the presence of antibodies to problematic foods.

It is also important to remember that IgE antibodies have a circulating half-life of 1-5 days, so any reaction shows current exposure to the antigen, meaning exposure within the several days immediately prior to collecting the test sample. The circulating half-life of IgG is approximately 21-24 days, which means that by approximately 3 months, antibodies to a particular food may be absent if the food has not been consumed by the patient. In other words, if the patient has not consumed the food prior to testing, no reaction to that food would be expected.

When running the Celiac and Gluten Sensitivity Profile, it is important to note that antibodies will only be present if the patient has consumed gluten prior to testing. If the patient is already on a gluten-free diet, genetic testing of the HLA DQ2/DQ8 genes may be helpful. According to the American College of Gastroenterology, a proposed gluten challenge after being gluten-free involves eating 3 grams of gluten daily for 8 weeks prior to testing. However, diagnostic changes are seen in most celiac disease patients after as little as 2 weeks of gluten ingestion.1

Pediatric Testing

It is recommended that a child be at least 1 year old before testing for IgG antibodies in order to eliminate the possibility of maternal antibodies influencing the results. Studies are lacking on the transfer of food-specific antibodies and/or the clinical significance of these maternal antibodies measured in the child's serum.

IgE antibodies do not cross the placenta, so there is no age restriction for IgE testing. According to Medscape, "For immunoglobulin (Ig) E-mediated allergy, there is no minimum age for testing, although it is important to consider age-related changes in patterns of sensitization. Sensitization to foods can occur in babies who are only a few weeks old. On contrast, it is unusual to develop sensitization to respiratory allergens before 2 or 3 years of age. Furthermore, in preschoolers, sensitization to indoor allergens (e.g., cat, dog, dust mites) is more common than sensitization to pollens. Considering these patterns, it is certainly reasonable to test children for food-specific IgE in early infancy if the history suggests food allergy."2

Breastfeeding can result in the transfer of maternal IgG and IgA antibodies to the child. However, studies are lacking on the transfer of food-specific antibodies and/or the clinical significance of these maternal antibodies measured in the child's serum.

The immune system continues to develop into childhood. Therefore, the clinical applicability of test results in pediatric patients may be unclear. What may be interpreted as an abnormal result for an adult, may be normal for an infant's developing immune system. This can be the case with other immune testing, including stool calprotectin and stool eosinophil protein X (EPX), where elevations would be expected in a healthy infant, but abnormal in an adult.

Diseases That May Affect Antibody Levels

Antibody testing may be inaccurate if the patient has liver disease, severe renal disease, protein-losing enteropathy, HIV infection, or other immunodeficiencies. In patients with selective IgA deficiency, celiac disease testing should include the IgG antibody against tissue transglutaminase (tTG) and deamidated gliadin (DGP), since the IgA antibody may not be detected or may be very low. Genova does not currently offer the IgG antibodies for tTG and DGP.

Viruses such as Epstein-Barr virus (EBV), rubella, and cytomegalovirus (CMV) can be associated with lower antibody levels.

Results may be skewed in patients with rheumatological pathologies associated with the production of heterophilic antibodies, such as rheumatoid factor (RF).

Diseases associated with a false positive tissue transglutaminase (tTG) IgA antibody on the celiac test may include type 1 diabetes, autoimmune liver disease, primary biliary cirrhosis, inflammatory bowel disease, connective tissue diseases, and HIV infection. Genetic testing of the HLA DQ2/DQ8 genes may be helpful in these patients.

References

  1. Rubio-Tapia A, et. al. ACG Clinical Guidelines: Diagnosis and Management of Celiac Disease. American Journal of Gastroenterology. 2013;108:656-676.
  2. Gern J. Allergy Testing in Children. Medscape. 2004. https://www.medscape.com/viewarticle/465526

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 — PATIENTS — 

Important Prep Before Patient Takes Test

Certain medications and/or foods may impact test results. Please consult with your healthcare provider before stopping any prescription or over-the-counter medications. Genova never recommends that patients discontinue medically necessary medications or supplements in order to complete testing. There may be times when your healthcare provider prefers that you stay on a medication during testing in order to evaluate its effectiveness. The following medications may influence test results:

  • glucocorticoids (e.g., oral prednisone, steroid metered-dose inhaler, cortisone cream)
  • chemotherapy
  • other immunosuppressive agents (e.g., Humira, Rituxan)
  • NSAIDS (e.g., Ibuprofen, Naproxen, Aspirin)
  • anticonvulsants (e.g., Carbamazepine, Valproate)
  • Omalizumab is a monoclonal antibody designed to bind to free serum IgE, which may influence test results
  • Heparin interferes with the measurement of tissue transglutaminase (tTG) antibodies on the celiac panel

Important: If a patient has a known IgE-mediated food allergy, Genova DOES NOT recommend exposure to the food that may cause a reaction. When testing for food antibodies, it is suggested that the patient eat a variety of foods for 2-3 weeks prior to testing (except for foods that are known to cause severe reactions). Doing so will help to ensure the presence of antibodies to problematic foods.

Antibody testing may be inaccurate if the patient has liver disease, severe kidney disease, protein-losing enteropathy from gastrointestinal tract damage, HIV infection, or other immunodeficiencies. Results may be skewed in patients with rheumatological pathologies associated with the production of heterophilic antibodies such as rheumatoid factor (RF).

It is recommended that a child be at least 1 year old before testing for IgG antibodies. There is no age restriction for IgE testing.


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