Medications That Can Affect Test Results
Certain medications may impact the results of the antibody test. It's important to note that the reference ranges were established based on people who were not taking any medications or supplements. In some cases, we may not know the potential impact of a medication on the test results.
Stopping essential medications or supplements for testing is not recommended. If needed, consult with your healthcare provider or book a consultation with a specialist.
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Sometimes, a person may need to continue taking a medication or dietary supplement during testing to assess its effectiveness. The recommendation to stop any substance is meant to establish a baseline for accurate results.
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If you choose to discontinue a medication, a general rule is to wait for the drug's biological half-life times 5 to allow for clearance before testing. With certain medications, the drug itself may have left the body, but its effects may linger.
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The following medications may influence the antibody test results, but they should not interfere with the ability to conduct the testitself:
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Glucocorticoids (e.g., oral prednisone, steroid metered-dose inhaler, cortisone cream);
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Chemotherapy;
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Other immunosuppressive agents (e.g., Humira, Rituxan);
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NSAIDs (e.g., Ibuprofen, Naproxen, Aspirin);
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Anticonvulsants (e.g., Carbamazepine, Valproate).
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These medications can either increase or decrease immunoglobulin levels and may lead to 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.
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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.
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Clinicians may use the allergen-specific IgE antibody test to monitor response to immunotherapy (desensitization).
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Length of Exposure to Antigens
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Important: In cases of a known IgE-mediated food allergy, exposure to the food that may trigger a reaction is strongly advised against.
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When testing for food antibodies, it's recommended that you consume a variety of foods for 2-3 weeks before the test, except for foods that are known to cause severe reactions. This helps ensure the presence of antibodies to problematic foods.
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Keep in mind that IgE antibodies have a circulating half-life of 1-5 days, which means they indicate recent exposure to the antigen, usually within several days before the test. On the other hand, IgG antibodies have a circulating half-life of approximately 21-24 days. This means that after about 3 months without consuming a specific food, antibodies to that food may no longer be detectable. In other words, if the person has not consumed the food prior to testing, no reaction to that food would be expected.
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When taking the Celiac Profile test, it's essential to note that antibodies will only appear if you've consumed gluten before testing. If you're already on a gluten-free diet, genetic testing of the HLA DQ2/DQ8 genes may be a helpful alternative. According to the American College of Gastroenterology, a gluten challenge after being gluten-free typically involves consuming 3 grams of gluten daily for 8 weeks before testing. However, diagnostic changes are often observed in most celiac disease patients after as little as 2 weeks of gluten consumption.
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Pediatric Testing
It is recommended that a child be at least 1 year old before testing for IgG antibodies to eliminate the possibility of maternal antibodies influencing the results. Studies are lacking on the transfer of food-specific antibodies and the clinical significance of these maternal antibodies measured in the child's serum.
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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. In 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.
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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 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 also 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 deemed abnormal in an adult.
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Diseases That May Affect Antibody Levels
Antibody testing may yield inaccurate results if the patient has underlying liver disease, severe renal disease, protein-losing enteropathy, HIV infection, or other immunodeficiencies. In cases of selective IgA deficiency, celiac disease testing should encompass the assessment of IgG antibodies against tissue transglutaminase (tTG) and deamidated gliadin (DGP), as IgA antibodies may either remain undetected or appear at very low levels.
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Viral infections such as Epstein-Barr virus (EBV), rubella, and cytomegalovirus (CMV) can potentially lead to reduced antibody levels.
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It's essential to note that results may be skewed in persons with rheumatological conditions associated with the production of heterophilic antibodies, such as rheumatoid factor (RF).
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Diseases linked to a false positive tissue transglutaminase (tTG) IgA antibody on the celiac test may encompass type 1 diabetes, autoimmune liver disease, primary biliary cirrhosis, inflammatory bowel disease, connective tissue disorders, and HIV infection. In these cases, genetic testing of the HLA DQ2/DQ8 genes may offer valuable insights.
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