Tissue transglutaminase, IgG antibodies
Why this test?
For screening, diagnosis and treatment control of gluten enteropathy in patients with isolated immunoglobulin A deficiency.
In what cases is it prescribed?
With symptoms of gluten enteropathy: periodic vomiting, diarrhea, growth retardation (in children), abdominal pain, anemia, epilepsy, atopic dermatitis, congestion in the corners of the mouth, canker sores, Dühring's herpetiform dermatitis, signs of vitamin deficiency (impaired vision, neuropathy, osteopenia , increased bleeding, amenorrhea, infertility, impotence (in adults).
When examining a patient with a heavy family history of gluten enteropathy or other risk factors for this disease.
When examining a patient with isolated immunoglobulin A deficiency.
When monitoring the treatment of gluten enteropathy.
Antibodies to tissue transglutaminase are a clinical and laboratory marker of gluten enteropathy (celiac disease). Autoantigen for them is the enzyme tissue transglutaminase, which is found in endothelial cells, hepatocytes, erythrocytes, as well as in the epithelium and submucosal layer of the small intestine. Tissue transglutaminase catalyzes the formation of bonds between different protein molecules, and one of its substrates can be food gliadin. Under the influence of tissue transglutaminase, it acquires immunogenic properties, which in susceptible individuals lead to inflammation of the intestinal mucosa. This autoimmune process is accompanied by atrophy of the intestinal mucosa and impaired absorption, which is manifested by signs of gluten enteropathy.
Antibodies to transglutaminase refer to immunoglobulins of class A or G. Analysis of anti-tTG, IgG is most important for the diagnosis of gluten enteropathy in patients with isolated immunoglobulin A deficiency. Gluten enteropathy is characterized by various immunological disorders, provoked by the intake of gluten protein with food. In this disease, several variants of autoantibodies have been described, including antibodies to gliadin, endomysium, and tissue transglutaminase.
Determination of these antibodies in blood serum is used to diagnose gluten enteropathy and control its treatment. Compared to other antibodies, anti-tTG are characterized by the highest sensitivity and specificity, which allows them to be considered the best indicator for the diagnosis of gluten enteropathy. Celiac disease is often combined with other diseases of the immune system, such as type 1 diabetes, Graves' disease, myasthenia gravis, and others. Of particular importance is the combination of gluten enteropathy and isolated deficiency of immunoglobulin A.
The frequency of isolated deficiency of immunoglobulin A in gluten enteropathy is higher than in the general population and is 2.6-3% (for comparison: in the general population - 0.2-0.25 %). This feature should be taken into account when interpreting the results of the analysis of IgA antibodies to gliadin, endomysium or tissue transglutaminase.
The result of determining any IgA in patients with isolated immunoglobulin A deficiency will be pseudonegative regardless of the presence or absence of gluten enteropathy. To avoid diagnostic errors, it is recommended to measure the concentration of anti-tTG, IgG in patients with symptoms of gluten enteropathy, especially if the result of the test for anti-tTG, IgA was negative. In addition, the complex of mandatory laboratory tests for celiac disease includes a study on total immunoglobulin A. Gluten enteropathy is transmitted genetically.
The disease is associated with certain alleles of HLA-DQ2 and HLA-DQ8. The prevalence of gluten enteropathy among relatives of a patient with this disease is much higher than the average in the population. Thus, the probability of detecting its signs in a relative of the first line of kinship is about 10%. Therefore, with a positive result of the analysis and confirmation of the diagnosis of gluten enteropathy, it is advisable to conduct a laboratory examination of the patient's family members. Other risk factors include type 1 diabetes, Down syndrome, and isolated immunoglobulin A deficiency. Isolated (selective) deficiency of immunoglobulin A is the most common type of congenital deficiency in humans. The disease occurs with a frequency of 1: 400-1: 500 in the population of Europeans.
With an isolated deficiency of immunoglobulin A, infections of the respiratory tract and diseases of the immune system (atopic dermatitis, rheumatoid arthritis, vitiligo) are more often observed. The frequency of gluten enteropathy is increased by 10-15 times. Screening for gluten enteropathy in patients with isolated immunoglobulin A deficiency cannot be performed with anti-tTG, IgA, or other celiac-specific antibodies related to class A immunoglobulins.
All patients with a combination of this immunodeficiency and gluten enteropathy test for anti-tTG , IgA will be negative. Therefore, the main test for screening gluten enteropathy in patients with isolated immunoglobulin A deficiency is the anti-tTG, IgG test. The specificity and sensitivity of this test is compared with the analysis for anti-tTG, IgA. The level of anti-tTG, IgG reflects disease activity. When following a gluten-free diet and achieving remission of the disease, the concentration of these antibodies gradually decreases and the analysis may become negative. Therefore, the anti-tTG, IgG test can be used to assess the patient's susceptibility to a gluten-free diet. For the same reason, it is recommended to give blood for analysis before prescribing a gluten-free diet.