Tissue Transglutaminase (tTG) Antibody IgA
What Is Tissue Transglutaminase Test?
It is the specific test for screening and diagnosing Celiac disease and an associated condition called dermatitis herpetiformis. Celiac disease is an autoimmune condition that means your body attacks itself.
Tissue transglutaminase is a catalyzing enzyme that modifies proteins' structure in your body. In patients with celiac disease, antibodies are formed against the tissue transglutaminases enzyme; these antibodies are used to diagnose this disease. These antibodies are termed anti-tissue transglutaminase antibodies. Although IgA isotype of antibody is predominant in this disease, individuals may produce IgG isotype, particularly those with IgA deficiency.
What Is The Test Used For?
It is one of several tests used to evaluate patients suspected of having celiac disease. Celiac disease is also known as celiac sprue, non-tropical sprue, and gluten-sensitive enteropathy. It is one of the most common autoimmune disorders, with a prevalence of 1% worldwide.
Celiac disease is an immune-mediated inflammatory disorder that occurs in genetically susceptible individuals after consuming "gluten" containing products like wheat, barley, and rye. These patients are allergic to "Gliadin," a protein component of gluten; it initiates a cascade of events and ultimately stimulates their immune system to destroy their body cells. Especially it affects small bowel cells called enterocytes, resulting in villous atrophy. Villi are small projections like fingers in the wall of the small intestine. They increase the intestine's surface area and help in the rapid absorption of nutrients. Celiac disease runs in families; there is a 3% increased risk of developing celiac disease in people with genes HLA DQ2 and HLA DQ8.
In children less than 2 years of age, the test remains insignificant in diagnosing celiac disease due to a lack of established immunity in children. So, some other tests are preferred to diagnose celiac disease in children.
MANIFESTATIONS OF CELIAC DISEASE:
1. Gastrointestinal symptoms:
- Abdominal pain
- Nausea vomiting
- Weight loss
2. Non-gastrointestinal symptoms:
- Growth failure (short stature, delayed onset of puberty)
- Nutritional deficiency of iron and vitamins leads to anemia
- Chronic fatigue (pain in muscle and joints)
- Recurrent miscarriages
- Recurrent mouth ulcers (aphthous ulcers, canker sores)
- Dental enamel hypoplasia
- Dermatitis herpetiformis (painful itchy blisters commonly occur over the abdomen)
3. Neuropsychiatric symptoms:
- Peripheral neuropathy (numbness and weakness in limbs)
- Seizures and epilepsy
Celiac disease is associated with other autoimmune conditions like Hashimoto's thyroiditis, Down syndrome, Turner syndrome, Selective IgA deficiency, Autoimmune liver disease, and Type 1 diabetes mellitus. Every individual with type 1 diabetes is almost always screened for celiac disease as they have a strong association. Moreover, it also increases the risk of developing Non-Hodgkin lymphoma.
What Is The Test Used For?
- This test is utilized to diagnose celiac disease with suspected signs and symptoms.
- For screening, if you have an increased risk for developing a celiac disease like positive family history, previous diagnosis of associated autoimmune disease, positive for HLA DQ2 and HLA DQ8 genes.
- For evaluation and screening of dermatitis herpetiformis, along with endomysial antibody tests.
- For monitoring how well you are doing with a gluten-free diet if you are diagnosed with celiac disease.
Definitive diagnosis of celiac disease requires jejunal biopsy (small bowel biopsy), which demonstrates villous atrophy. But it is an invasive procedure and is also costly. Therefore, serological and genetic tests are recommended first to define the disease, and those who came positive are referred for small intestinal biopsy, limiting the number of unnecessary procedures.
What Type Of Sample Is Required?
A blood sample (serum) is required. Your healthcare provider will use a needle to obtain a small amount of blood from the vein of your arm. The sample is collected in a test tube or vial and sent to the laboratory.
Do You Need To Prepare For This Test?
For the test to be accurate, you must be on a gluten-containing diet to form enough antibodies against tissue transglutaminase, which could be detected easily. If you have IgA deficiency, the result may show false-negative; in this scenario, the IgG isotype of antibodies is tested for accurate results. The test may reveal false-positive results in some autoimmune diseases, including rheumatoid arthritis, psoriatic arthritis, Hashimoto's thyroiditis, etc.
If the test is used to check how well you are doing with the gluten-free diet, no special preparation is needed.
This test results may not be error-free for children less than 2 years of age, as they don't have established immunity for this test.
Is There Any Risk To This Test?
No significant risk is related to this test. Since a needle is used to prick, you might feel stung and pain at the site of the prick. Very seldom, you may experience lightheadedness, bruising, and bleeding from the site of the prick. Rarely, the infection may occur.
What Does Test Result Means?
The test results are usually obtained between 1-4 days and are usually termed as negative and positive.
- A positive test means that you have higher levels of anti-transglutaminase antibodies (IgG or IgA>15U/ml) in your blood. That strongly indicates that you have celiac disease or its associated disorder.
- A negative test means that you have a lower level of antibodies (IgG or IgA <15U/ml) in your blood. This lower level of anti-transglutaminase antibodies excludes the presence of celiac disease.
- Children are the exception, as they may come up with negative results even with celiac disease.
Keep in mind that one test cannot definitely diagnose Celiac disease; your healthcare provider may retest you or order a new test for a better diagnosis. Should you have any questions regarding your test results, you must consult your healthcare provider.
- Deamidated gliadin antibody test: a diagnostic test for celiac disease in patients with IgA deficiency.
- IgA endomysial antibody test (EMA): 98% specific test, but it is expensive.
- Total serum IgA
- Intestinal fatty acid-binding protein test
- Video capsule endoscopy
- Genetic testing for HLA DQ2 and HLA DQ8
- Small intestinal biopsy
- Thyroid function test