From the Guidelines
Blood tests for evaluating gluten sensitivity include tissue transglutaminase antibodies (tTG-IgA), total serum IgA, deamidated gliadin peptide antibodies (DGP IgA and IgG), and endomysial antibodies (EMA), with tTG-IgA being the most sensitive and specific initial screening test for celiac disease, as supported by the most recent guidelines 1. The diagnosis of celiac disease (CD) and non-celiac gluten sensitivity (NCGS) relies on a combination of clinical evaluation, serological tests, and intestinal biopsy.
- The tTG-IgA test is the preferred initial screening test for CD, with a sensitivity of about 93% and specificity of 98% 1.
- Total serum IgA should be measured alongside tTG-IgA because IgA deficiency is more common in celiac patients, which could lead to false-negative results.
- If IgA deficiency is present, DGP-IgG testing is recommended as an alternative, as it can help identify patients with CD who may have false-negative tTG-IgA results.
- EMA testing is highly specific but more expensive and subjective to interpret, and is often used as a second-line test to confirm the diagnosis of CD.
- For accurate results, patients should continue consuming gluten before testing, as eliminating gluten can normalize antibody levels and lead to false-negative results.
- Genetic testing for HLA-DQ2 and HLA-DQ8 can help rule out celiac disease but cannot confirm it, as the presence of these genes is necessary but not sufficient for the development of CD 1.
- It's essential to note that blood tests alone cannot definitively diagnose celiac disease; an intestinal biopsy is typically required for confirmation after positive blood tests, especially in cases where the diagnosis is uncertain or the patient has a complex clinical presentation 1.
From the Research
Blood Tests for Gluten Sensitivity
The following blood tests are used to evaluate for gluten sensitivity, specifically for celiac disease (CD) and non-celiac gluten sensitivity (NCGS):
- Tissue transglutaminase antibodies (tTG) 2, 3, 4, 5
- Endomysial antibodies (EMA) 2, 3, 5
- Deamidated gliadin peptide antibodies (DGP) 6
- Antigliadin antibodies (AGA) 2, 5
Celiac Disease (CD) Diagnosis
For CD diagnosis, the following tests are used:
- tTG IgA assay: high specificity (0.83) but low sensitivity (0.50) in detecting persistent villous atrophy 3
- EMA IgA assay: high specificity (0.91) but low sensitivity (0.45) in detecting persistent villous atrophy 3
- DGP antibody testing: can identify cases of CD in tTG-negative individuals, although the positive predictive value is low 6
Non-Celiac Gluten Sensitivity (NCGS) Diagnosis
There are no specific blood tests mentioned in the provided studies for NCGS diagnosis. However, the studies suggest that the tests used for CD diagnosis may not be suitable for NCGS diagnosis.
Test Characteristics
The characteristics of the blood tests used for gluten sensitivity are:
- tTG autoantibody ELISA: highly sensitive (129/136) and specific (194/207) in detecting CD 4
- EMA test: considered the "gold standard" of serological CD markers, but may not be automated and depends on subjective fluorescence display 2
- DGP antibody testing: has sensitivity and specificity comparable to tTG testing, and can identify cases of CD in tTG-negative individuals 6