Tissue transglutaminase, IgA antibodies
Why this test?
For the celiac disease diagnosis with patients who have clinical symptoms of this disease.
For screening of celiac disease with risk factors patients (hereditary history of celiac disease, type 1 diabetes, Down syndrome).
To assess the patient's adherence to a gluten-free diet and disease activity.
In what cases is it prescribed?
With symptoms of celiac disease: periodic vomiting, diarrhea, growth retardation (in children), abdominal pain, anemia, epilepsy, atopic dermatitis, angular cheilitis, aphthae, Dühring's herpetiform dermatitis, signs of vitamin deficiency - visual impairment, neuropathy, osteopenia, increased bleeding , amenorrhea, infertility, impotence (in adults);
when examining a patient with a heavy family history of celiac disease;
in the control of treatment of celiac disease;
when examining a patient with type 1 diabetes, Hashimoto's autoimmune thyroiditis, total alopecia, systemic connective tissue diseases, and Down syndrome.
Antibodies to tissue transglutaminase IgA are the best clinical and laboratory marker of gluten enteropathy. Tissue transglutaminase is an enzyme that catalyzes the formation of bonds between various protein molecules rich in glutamine and lysine. It is present in many tissues, including the submucosa of the gastrointestinal tract. Gliadin, which comes with food as part of gluten, consists of 40% of the amino acid glutamine and can act as a substrate for tissue transglutaminase. Under the action of this enzyme, gliadin is transformed into a more immunogenic peptide. In people prone to celiac disease, the use of gluten and the formation of a modified form of gliadin is accompanied by an inflammatory reaction with subsequent atrophy of the intestinal mucosa.
Clinically, this autoimmune process manifests as gluten enteropathy (celiac disease). Celiac disease is a chronic inflammatory bowel disease in which various autoantibodies to gliadin, endomysium and tissue transglutaminase can be detected in the blood.
Despite some features of the clinical picture of the disease, the symptoms of celiac disease can resemble syndromes observed in irritable bowel syndrome, cystic fibrosis, chronic pancreatitis, and many other diseases of the gastrointestinal tract. In the differential diagnosis of celiac disease, serological tests are of great importance, allowing to distinguish this disease from other conditions accompanied by diarrheal syndrome.
The main purpose of serological tests for suspected celiac disease is to identify patients who are indicated for endoscopy and biopsy of the small intestine for histological verification of the diagnosis. This analysis is characterized by high sensitivity (81-100%) and specificity (97-99%), which allows us to consider it the best method that meets this goal.
With a positive test result, endoscopy is recommended in patients with clinical signs of celiac disease. It should be noted that a negative result does not completely rule out the disease. If a negative result is obtained in a patient with pronounced clinical signs of celiac disease, an additional analysis is recommended - a test for antibodies to endomysium, IgA. Quite often, celiac disease is asymptomatic or characterized by nonspecific symptoms (unmotivated weakness, shortness of breath, changes in the skin, hair, nails) that indicate anemia or malabsorption.
Despite the absence of bright manifestations in this course of the disease, chronic malabsorption can lead to a deficiency of trace elements and vitamins and to irreversible changes, such as osteoporosis (vitamin D deficiency) and slowing of skin regeneration (zinc deficiency).
In addition, celiac disease is associated with the development of T-cell lymphoma of the intestine. In order to recognize asymptomatic celiac disease in time and prevent complications, screening for this disease is carried out in patients with risk factors (once every two years). Since the level of IgA antibodies can change over time, it is recommended to repeat the analysis if the result is negative. A positive test result may be an indication for a diagnostic biopsy.
Diagnosis of celiac disease in patients with isolated deficiency of immunoglobulin A presents a certain difficulty. The prevalence of this form of congenital immunodeficiency among patients with celiac disease is higher than among healthy people, and is 2-3%. Since patients with isolated IgA deficiency do not produce this immunoglobulin at all, the result of the test for anti-tTG IgA in them will be pseudonegative. In view of this feature, the anti-tTG IgA test should be supplemented with an anti-tTG IgG test. Analysis of total immunoglobulins of class A is also recommended. The level of anti-tTG reflects disease activity. When following a gluten-free diet and achieving remission, the concentration of these antibodies gradually (usually within 6-12 months) decreases, and the analysis may become negative.
Therefore, the anti-tTG IgA test is also used to assess a patient's adherence to a gluten-free diet. Celiac disease often coexists with other autoimmune diseases, such as type 1 diabetes, Hashimoto's autoimmune thyroiditis, and systemic connective tissue diseases.
Therefore, the examination of a patient with celiac disease includes additional laboratory tests that exclude concomitant diseases. Anti-tTG IgA analysis is also carried out during the examination of patients with Down syndrome, given the frequent occurrence of celiac disease among them.