Blood testing for celiac disease - nutrition celiac

The diagnosis of celiac disease is a complex process that requires the performance of various tests to confirm or rule out its existence. These tests are essential to identify individuals who may be suffering from the disease and to ensure a proper diagnosis.

Serological tests can detect specific antibodies that are produced in response to gluten. These antibodies can be measured in the blood, and their presence suggests the possibility that celiac disease is present.

Serology is the most common test in cases of suspected celiac disease. However, these tests are not conclusive, as some antibodies may appear from other causes or may not be elevated in all patients.

In addition to antibody screening, genetic testing can also be performed to identify the HLA DQ2 and HLA DQ8 antigens, which are associated with celiac disease. This test can help rule out the disease if the result is negative. A positive result indicates an increased likelihood of having celiac disease, although it does not confirm it, it simply suggests a genetic predisposition to develop celiac disease.

Antibody Detection Tests

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

The antigliadin antibody test [AGA] for IgA and IgG looks for specific antibodies generated in response to gliadin, a gluten protein. However, this test is not very accurate and can result in false positives and negatives.

The anti-tissue transglutaminase [tTG] antibody test for IgA is the most commonly used test for celiac disease. This test measures antibodies produced in response to tissue transglutaminase, an enzyme present in the small intestine, and is more accurate than the AGA test, showing high sensitivity and specificity.

The IgA anti-endomysial antibody [EMA] test looks for antibodies that respond to endomysial tissue, which surrounds the muscles of the small intestine. This test is very specific and is used to confirm the results of the tTG test.

Possible Causes of False Negative Results

Serologic tests for celiac disease antibodies can give negative results for a variety of reasons:

• Timing of the test: antibody levels can vary, and if the test is performed when these are low, it may give a negative result. It is advisable to test at different times or combine with other tests for a more accurate diagnosis.

• Gluten consumption: The disease is triggered by gluten intake in genetically predisposed individuals. If a person follows a gluten-free diet prior to testing, antibody levels may decrease, resulting in a negative result. It is recommended to follow the physician's instructions.

• IgA deficiency: Approximately 1% of celiac disease patients may have immunoglobulin A [IgA] deficiency, which affects the accuracy of IgA-based testing. In these cases, tests that measure other types of antibodies, such as IgG, may be used.

• Technical errors: As with any laboratory test, errors can occur, such as mislabeled samples or handling problems, which can lead to false negative results.

Importance of Antibody Types in Detection

The immune system of a person with celiac disease is sensitive to gliadin, part of the gluten protein. In this condition, specific antibodies are generated to fight it. The selection of antibodies used in testing is crucial, as some are more specific and sensitive for the disease.

Anti-gliadin [AGA], anti-tissue transglutaminase [tTG] and anti-endomysial [EMA] antibodies are markers detected mainly in the immunoglobulin A [IgA] subtype.

IgA is localized in mucous membranes, such as in the small intestine. Since celiac disease affects this organ, the detection of IgA antibodies is more accurate in confirming the disease. However, a percentage of people with celiac disease have IgA deficiency, which can affect the accuracy of the results and give false negatives.

For those who do not produce normal amounts of IgA, IgG can be used, which, although less sensitive, helps detect IgA deficiency and other autoimmune diseases. This may cause results to vary in these at-risk groups.

If the antibody test results are negative but celiac disease is suspected, it is recommended to proceed with an intestinal biopsy. If this is positive, an endoscopy and intestinal biopsy should be performed to confirm celiac disease and assess damage to the small intestine.

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