Blood tests to detect celiac disease

The diagnosis of celiac disease is a complex process that requires a series of tests to confirm or rule out the presence of the disease. These tests are an important tool to identify people who may have the disease and to make a proper diagnosis.

Serological screening tests for celiac disease are used to look for specific antibodies that are produced in the body in response to gluten. These antibodies can be measured in the blood, and if present, indicate the possibility that celiac disease is present.

Serology is the most common test and the one that is usually performed first if celiac disease is suspected. However, these tests are not sufficient to make a definitive diagnosis, as some antibodies may be present for other reasons, or the person may not raise antibodies.

In addition to antibody screening tests, a genetic test can also be used to detect the human leukocyte antigens HLA DQ2 and HLA DQ8, which are associated with celiac disease. It is useful to help rule out the disease if the result is negative. If positive, it increases the likelihood of having celiac disease, although it does not confirm it. It only implies that you have the genetic predisposition to develop it.

Antibody detection tests

There are several tests that can be performed to detect the presence of antibodies in the blood.

The anti-gliadin antibody test (AGA) for IgA and IgG: is a test that looks for specific antibodies that are produced in response to gliadin, a protein in gluten. However, this test is not very accurate and can result in false positives and false negatives.

The anti-tissue transglutaminase (tTG) antibody test for IgA is the most commonly used screening test for celiac disease. This test looks for specific antibodies that are produced in response to tissue transglutaminase, an enzyme present in the small intestine. This test is more accurate than the AGA test and has a high sensitivity and specificity.

The IgA anti-endomysial antibody (EMA) test: This test looks for antibodies that are produced in response to endomysial tissue, which is a tissue that surrounds the muscles of the small intestine. This test is very specific and is used to confirm the results of the tTG test.

What can cause a false negative?

Serology tests for celiac disease antibodies can give negative results for a number of reasons, including:

• Timing of testing: antibody levels can vary over time, and it is possible for a serology test to be performed at a time when antibody levels are low or undetectable. Testing at different times or in combination with other tests is recommended to obtain a more accurate diagnosis.
• Gluten consumption: This disease is triggered by gluten ingestion in genetically susceptible individuals. If a person is following a gluten-free diet at the time of testing, antibody levels may decrease or disappear, which could result in a negative result. It is recommended that they follow their physician's instructions.
• IgA deficiency: About 1% of people with celiac disease may be deficient in immunoglobulin A (IgA), which is the most common antibody class used in serology testing for celiac disease. In these cases, alternative tests based on other types of antibodies, such as IgG antibodies, may be used.
• Other technical errors: As with any laboratory test, there is the possibility of technical errors, such as mislabeled samples, errors in sample handling or problems in test performance, which could lead to false negative results.

Importance of antibody types in the screening test

The immune system of a person with celiac disease is sensitive to gliadin, which is part of the protein present in gluten. The body of a person with celiac disease produces antibodies to fight it. The type of antibodies used in screening tests for celiac disease is important because certain antibodies are more specific and sensitive for this particular disease.

Anti-gliadin antibodies (AGA), anti-tissue transglutaminase antibodies (tTG) and anti-endomysial antibodies (EMA) act as markers, and can be detected mostly in the immunoglobulin A (IgA) subtype.

IgA is a class of antibody found in mucous membranes, including the lining of the small intestine. Because celiac disease primarily affects the small intestine, detection of IgA antibodies may be more accurate in confirming the presence of the disease. However, at least 1% of people with celiac disease also have IgA deficiency which can affect the accuracy of the results, and lead to false negatives in the case of an overlap between these two conditions.

In the case of persons who do not produce normal amounts of IgA antibody, IgG can be used which, although not very sensitive to celiac disease, is useful for detecting IgA deficiency and the presence of other autoimmune diseases. For this reason, results may vary from positive to negative in these risk groups.

If the antibody screening test is negative, but it is suspected that the person may have celiac disease because of genetics or other reasons, the next step is to perform an intestinal biopsy.

If the result is positive, an endoscopy and intestinal biopsy should also be performed to confirm celiac disease and determine the damage to the small intestine accurately.