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A tissue transglutaminase IgA and/or IgG test, also referred to as the tTG blood test, may be performed when trying to diagnose certain autoimmune diseases, especially celiac disease. When a patient has celiac disease, their bodies will produce two different antibodies, immunoglobulin G and immunoglobulin A, that attack tTG. If a patient's doctor suspects that a patient may be suffering from celiac disease, they may request this test as part of the diagnostic process.
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Preparation and Procedure
Some preparation is needed to ensure accurate test results. The patient should be eating a diet in which foods that contain gluten are present, such as pastas and breads. If a gluten-free diet is being followed there will not be any measurable antibody response, resulting in inaccurate test results.
To obtain a testing sample, the patient's health care provider will have to draw blood from a vein. This is done by using a needle, typically a butterfly needle, and carefully inserting it into a vein. The veins in the arm, hand, or crook of the elbow are most often used. Once the needle is in place, a small tube will collect a sample of blood, then the needle is removed. If this test is being done on a baby, the health care provider may prick the baby's foot with a lancet and allow some blood to collect in a vial.
For most patients, this is not painful, though slight discomfort may occur. After the blood is collected, the patient may experience some bruising at the puncture site that is temporary.
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Most patients will wait a day or two to get their results. If the patient's test results are positive, it could indicate that the patient has celiac disease. It may also indicate that the patient has a condition known as dermatitis herpetiformis. If the results are strong or moderate, it is more likely that celiac disease is present. The tTG blood test cannot give a definitive diagnosis, therefore, if the results indicate celiac disease, a biopsy will most likely be performed to confirm this diagnosis. In addition to a biopsy, the patient's doctor may also perform the following tests:
- Upper endoscopy
- Albumin levels
- Clotting factor
- Cholesterol levels
- Liver enzymes
- Alkaline phosphatase
- Complete blood count
- Prothrombin time
Dermatitis herpetiformis is a condition characterized by a chronic, itchy rash with blisters and bumps. If this condition is suspected, a direct immunofluorescence test and biopsy of the skin may be done to confirm the diagnosis. An intestine biopsy may also be recommended.
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KidsHealth from Nemours. (2010). Blood Test: Tissue Transglutaminase IgA, IgG. Retrieved on October 15, 2010 from KidsHealth from Nemours: http://kidshealth.org/parent/system/medical/test_ttg.html
Dahlbom, I., et al. (2005). Immunoglobulin G (IgG) Anti-Tissue Transglutaminase Antibodies Used as Markers for IgA-Deficient Celiac Disease Patients. Retrieved on October 15, 2010 from the American Society for Microbiology via PubMed Central: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC549312/