Other blood tests look for different indicators, including fatty acid-binding protein (I-FABP) and certain genetic markers.
When a celiac blood test is positive, further testing is necessary. The only way to definitively diagnose celiac disease is with a biopsy of the small intestine to look for damage to the tissue.
This article reviews tests done for celiac disease screening and what they reveal.
Antibody Tests
There are four antibody tests for celiac disease. The most sensitive screen for immunoglobulin A (IgA)—the antibody most prominent in celiac.
People who are IgA-deficient (notably those with autoimmune disorders such as lupus or rheumatoid arthritis may be tested for immunoglobulin G (IgG) rather than IgA.
Tissue Transglutaminase (tTG)
The tTG test, also known as the anti-tissue transglutaminase test or anti-tTG, is the first-line option for antibody testing. tTG is an enzyme that plays a role in wound healing, cell-to-cell adhesion, the regulation of cell survival and death, and other biological processes.
It also is involved in the breakdown of gliadin—a water-soluble protein in gluten that’s essential for bread to rise during baking and that is easily absorbed by the intestines.
The interaction between tTG and gliadins is complex. After tTG breaks down gluten, the subsequent breakdown of gliadins in the bloodstream will activate tTG in the small intestine, causing enzyme levels to increase.
In response, the immune system produces defensive tTG antibodies that can be detected by the tTG test.
Deamidated Gliadin Peptide (DGP)
Deamidated gliadin is produced when tTG breaks down gliadin in the digestive tract. In people with celiac disease, this response is amplified and provides a key marker for the disease.
The deamidated gliadin peptide (DGP) test is able to detect deamidated gliadin IgA with a specificity of 94%, but a less-than-ideal sensitivity of 74%.
Because of this, it is most often used in tandem with the tTG test to provide early evidence of celiac disease, especially in children age 2 and under whose immune systems are not fully developed.
Endomysial Antibody (EMA)
Endomysial antibodies are produced in a layer of tissue surrounding muscles called the endomysium which contains a form of tTG that, when exposed to gluten, will activate and churn out antibodies in an autoimmune response.
The endomysial antibody (EMA) test is considerably more accurate than either the tTG or DGP test. It’s also more complicated and expensive.
Because the antibodies bind with smooth muscles, frozen esophageal or umbilical cord tissue is needed to draw the antibodies from the blood sample in high enough concentrations to elicit an accurate result.
The EMA test is primarily used to detect IgA antibodies, although an IgG version is also available.
Total Serum IgA
The total serum IgA test is used to check for IgA deficiency, which can cause a false-negative tTG-IgA or EMA reading. It is often used when a person tests negative for one or both of these tests.
Celiac blood test results are usually returned within one to three days, but the EMA and celiac genetic test results may take longer.
At other times, it is performed alongside the tTG to establish whether there is some degree of IgA deficiency that might otherwise influence the results.
If a total serum IgA test detects a deficiency of IgA, it will likely be followed by either a DGP-IgG test or a tTG-IgG test.
Other Blood Tests
Besides the antibody-based tests for celiac disease, there are two other blood tests that may be done before an intestinal biopsy is considered.
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Intestinal Fatty Acid-Binding Protein (I-FABP)
The I-FABP test detects a protein that is released into the blood whenever the intestines are damaged, as is characteristic of celiac disease.
Elevations of I-FAGP in blood may be evidence of celiac disease even if antibody tests are inconclusive. Urine samples can also be tested for I-FABP.
Celiac Genetic Testing
Celiac genetic testing, also known as HLA typing, is able to detect gene complexes called human leukocyte antigens (HLA) that may predispose a person to celiac disease, namely HLA-DQ2 and HLA-DQ8.
A positive genetic test result does not mean that you have celiac disease, since 55% of the general population have HLA-DQ2 and HLA-DQ8 compared to 98% of the celiac population But it can exclude celiac disease as a cause if neither of the antigens is detected.
