Generality
The blood dosing of anti-gliadin antibodies (AGA), introduced in clinical practice in the early 1980s, is a valuable aid in screening patients with suspected gluten-sensitive enteropathy ( celiac disease ).
In recent years, the importance of anti-gliadin antibodies for the diagnosis of celiac disease has been reduced by the advent of serological markers endowed with greater sensitivity and specificity, such as anti-endomysial autoantibodies (EmA) and anti-transglutaminase autoantibodies (tTGA ).
Celiac disease is a disease triggered by the ingestion of gluten; this protein is contained mainly in wheat, rye, oats and barley. In genetically predisposed subjects, the ingestion of gluten is not tolerated by the intestinal mucosa. This occurrence determines an inflammatory and immune reaction, which thins the intestine wall and, over time, does not allow to properly absorb the nutrients contained in the food taken. In the organism affected by celiac disease there is also an altered immune system response, which determines the formation of auto-antibodies against gluten (called AGA, anti-gliadin antibodies) and against the intestinal mucosa (EMA or tTG).
Celiac disease can affect any age, since it affects children and adults indiscriminately.
What's this
Gliadin is a part of gluten, a protein found in almost all cereals (especially wheat, but also rye, oats and barley).
Gliadin is a protein sub-fraction of gluten; it would however be more correct to speak of gliadins, since there are different forms or protein components, slightly different from each other and divided into four fractions based on the molecular weight and the electrophoretic response: α, Β, γ and ω.
The digestion of gluten ingested by the diet generates peptides (ie smaller molecules), such as gliadin, which can induce a specific response by IgG and IgA.
Anti-gliadin antibodies are autoantibodies produced as part of an immune response against gliadin, which occurs in people who are sensitive to gluten and exposed to it for a certain period of time.
For this reason, gliadin is believed to be one of the major culprits in the abnormal immune response leading to atrophy of intestinal villi in celiac disease. Excluding gluten from the diet of people with the disease, in fact, there is a rapid improvement and healing of small bowel lesions.
Why do you measure
The AGA dosage recognizes the presence of antibodies that trigger the inflammatory and immune reaction underlying celiac disease.
This laboratory test therefore contributes to the diagnosis of celiac disease and allows the monitoring or treatment of a gluten-free diet (gluten free).
The examination is indicated by the doctor in the presence of symptoms that suggest the presence of celiac disease, including:
- Episodes of diarrhea and vomiting;
- Abdominal pain;
- Anemia;
- Weight loss;
- Muscle weakness;
- Poor appetite.
AGA research is also useful for the diagnosis of celiac disease in children under the age of two with dubious or negative anti-transglutaminase (tTG) antibodies, and in cases of IgA deficiency.
Normal values
Normally, anti-gliadin antibodies are absent (ie the AGA search gives a negative result).
AGA Alti - Causes
Anti-gliadin antibodies are moderately elevated or significantly increased in gluten sensitive individuals. In general, if the test is positive, the diagnosis of celiac disease is likely.
AGA Bass - Causes
Low levels of anti-gliadin antibodies are not usually associated with medical problems and / or pathological consequences, therefore they are not considered clinically relevant.
How to measure it
The search for anti-gliadin antibodies (AGA) is carried out through a simple blood sample to be taken fasting.
Preparation
The dosage of anti-gliadin antibodies is a laboratory analysis that does not require any specific preparation. Taking medication does not affect the outcome of the test, but your doctor may indicate that you are fasting for at least 8 hours before taking the test.
Interpretation of Results
If the search for anti-gliadin antibodies is "negative" or "absent", it means that the person does not suffer from celiac disease. A "positive" or "present" outcome indicates, instead, the presence of the disease.
However, it should be noted that the test can easily be positive even in inflammatory bowel diseases not caused by gluten intolerance.
Sensitivity and Specificity of the exam
The finding in serum of anti-gliadin antibodies is suggestive of celiac disease, but it is not very sensitive, nor very specific.
In the serum of celiac patients anti-gliadin antibodies are detected both in the IgA class and in the IgG class, whereas in allergic subjects anti-gliadin antibodies of the IgE class can be found.
Anti-gliadin antibodies of the IgG class are slightly more sensitive but less specific markers compared to those of the IgA class (they are therefore able to identify a greater number of celiacs but tend to consider such a higher percentage of healthy patients as well). Anti-gliadin antibodies of the IgA class are slightly less sensitive but clearly more specific.
Test | Sensitivity * | Specificity* |
AGA IgG | 82-87% | 67-80% |
AGA IgA | 80-85% | 88-92% |
The greater sensitivity of the anti-gliadin IgG antibodies is due to the not negligible percentage of celiacs which does not produce IgA; in particular, the dosage of AGA IgG can be limited to the identification of subjects with IgA deficiency, and in children under two years, in which the IgA class is still poorly represented.
In general, under three years of age, anti-gliadin antibodies retain a very high diagnostic importance, since the antibody response to gliadin is the first to appear in order of time after the introduction of gluten.
This explains why serum IgA levels are generally detected together with serological markers of celiac disease.
- AGA positive fakes are frequent in subjects with protracted post-enteric diarrhea, inflammatory bowel diseases, Down syndrome, cystic fibrosis, allergies and other pathologies.
- AGA IgG fake positives are common in patients with irritable bowel syndrome, in subjects with autoimmune disease and also in a non-negligible percentage of healthy subjects.
Recently, laboratory tests for AGA dosing have been developed, using deamidated gliadin peptides, which have shown superior diagnostic accuracy for celiac disease compared to standard antigliadin tests. In particular, the test for the determination of deamidated synthetic peptide-binding antibodies (DGP) allows the significant recovery of the so-called "false positives", showing a sensitivity greater than 90% in addition to an undoubtedly improved specificity.
Although the importance of AGAs in celiac disease diagnostics is currently declining, anti-gliadin antibodies of the IgA class retain a prominent role in monitoring the celiac's response to a gluten-free diet; in general, after 3-6 months of diet therapy there is a disappearance of AGA IgA, while later (12-18 months) AGA IgG is reduced. A persistent positivity, even at low titer, indicates a reduced compliance of the patient with the gluten-free diet.
