Celiac Disease Blood Test: What to Ask Your Doctor For

What blood tests are used to screen for celiac disease?

The recommended first-line screening test is the tissue transglutaminase IgA antibody (tTG-IgA). When someone with celiac disease eats gluten, their immune system produces this antibody. It is highly sensitive and specific for celiac disease and is the test recommended by current guidelines 1Ref 1Rubio-Tapia A, Hill ID, Semrad C, Kelly CP, Greer KB, Limketkai BN, Lebwohl B (2023).American College of Gastroenterology Guidelines Update: Diagnosis and Management of Celiac Disease.tTG-IgA as first-line test, total IgA validation, IgA deficiency management, DGP-IgG alternative, confirmatory biopsy requirement in adults, gluten challenge, and HLA testing.

Because the tTG-IgA test relies on IgA antibodies, it can give a false-negative result in people with IgA deficiency — a relatively rare but important condition. For this reason, a total serum IgA level is often measured at the same time. If IgA deficiency is present, a tTG-IgG or deamidated gliadin peptide IgG (DGP-IgG) test can be used instead 1Ref 1Rubio-Tapia A, Hill ID, Semrad C, Kelly CP, Greer KB, Limketkai BN, Lebwohl B (2023).American College of Gastroenterology Guidelines Update: Diagnosis and Management of Celiac Disease.tTG-IgA as first-line test, total IgA validation, IgA deficiency management, DGP-IgG alternative, confirmatory biopsy requirement in adults, gluten challenge, and HLA testing.

What to specifically ask your doctor for: - Tissue transglutaminase IgA (tTG-IgA) - Total serum IgA (to validate the tTG-IgA result)

Are there other celiac antibody tests?

Yes, and your clinician may order a full celiac panel depending on the clinical picture 1Ref 1Rubio-Tapia A, Hill ID, Semrad C, Kelly CP, Greer KB, Limketkai BN, Lebwohl B (2023).American College of Gastroenterology Guidelines Update: Diagnosis and Management of Celiac Disease.tTG-IgA as first-line test, total IgA validation, IgA deficiency management, DGP-IgG alternative, confirmatory biopsy requirement in adults, gluten challenge, and HLA testing:

• Endomysial antibody IgA (EMA-IgA): Highly specific; may be added when tTG-IgA is weakly positive
• Deamidated gliadin peptide IgG (DGP-IgG): Useful when IgA deficiency is present, or in young children
• Anti-gliadin antibodies (AGA): Older, less specific tests that are generally not used in current diagnostic practice

For most adults presenting with symptoms, the tTG-IgA plus total IgA is the recommended starting point.

Why must you be eating gluten for the test to work?

This is critical: if you have already eliminated gluten from your diet, the antibody levels will fall and the test may come back falsely negative.

Celiac antibodies are produced in response to ongoing gluten exposure. When gluten is removed, the immune activation quiets down and antibody levels drop — sometimes within weeks to months 1Ref 1Rubio-Tapia A, Hill ID, Semrad C, Kelly CP, Greer KB, Limketkai BN, Lebwohl B (2023).American College of Gastroenterology Guidelines Update: Diagnosis and Management of Celiac Disease.tTG-IgA as first-line test, total IgA validation, IgA deficiency management, DGP-IgG alternative, confirmatory biopsy requirement in adults, gluten challenge, and HLA testing2Ref 2National Institute of Diabetes and Digestive and Kidney Diseases (2023).Celiac Disease.Under-diagnosis of celiac disease, importance of gluten consumption before testing, and consequences of a false-negative result on a gluten-free diet.

If you have already started a gluten-free diet, let your clinician know. They will discuss whether to proceed with a gluten challenge (deliberately reintroducing gluten for a period before testing) or to pursue other diagnostic options, such as HLA genetic testing 1Ref 1Rubio-Tapia A, Hill ID, Semrad C, Kelly CP, Greer KB, Limketkai BN, Lebwohl B (2023).American College of Gastroenterology Guidelines Update: Diagnosis and Management of Celiac Disease.tTG-IgA as first-line test, total IgA validation, IgA deficiency management, DGP-IgG alternative, confirmatory biopsy requirement in adults, gluten challenge, and HLA testing.

What happens if the blood test is positive?

A positive tTG-IgA is a strong signal but not a final diagnosis. Current guidelines require confirmation with a small intestinal biopsy in most adults 1Ref 1Rubio-Tapia A, Hill ID, Semrad C, Kelly CP, Greer KB, Limketkai BN, Lebwohl B (2023).American College of Gastroenterology Guidelines Update: Diagnosis and Management of Celiac Disease.tTG-IgA as first-line test, total IgA validation, IgA deficiency management, DGP-IgG alternative, confirmatory biopsy requirement in adults, gluten challenge, and HLA testing. During an upper endoscopy (EGD), a gastroenterologist takes small tissue samples from the duodenum (the first part of the small intestine). Characteristic findings — blunted intestinal villi (villous atrophy), increased intraepithelial lymphocytes — confirm celiac disease.

Biopsy remains the standard in most cases because: - Other conditions can cause elevated tTG-IgA (type 1 diabetes, liver disease, heart failure) - Confirmation matters before committing to a strict lifelong gluten-free diet 2Ref 2National Institute of Diabetes and Digestive and Kidney Diseases (2023).Celiac Disease.Under-diagnosis of celiac disease, importance of gluten consumption before testing, and consequences of a false-negative result on a gluten-free diet - A documented diagnosis is needed for insurance purposes and for monitoring

In children with a very high tTG-IgA level (more than 10 times the upper limit of normal), some guidelines allow diagnosis without biopsy — but in adults, biopsy is still recommended 1Ref 1Rubio-Tapia A, Hill ID, Semrad C, Kelly CP, Greer KB, Limketkai BN, Lebwohl B (2023).American College of Gastroenterology Guidelines Update: Diagnosis and Management of Celiac Disease.tTG-IgA as first-line test, total IgA validation, IgA deficiency management, DGP-IgG alternative, confirmatory biopsy requirement in adults, gluten challenge, and HLA testing.

What should I do if I suspect celiac disease but my doctor hasn't tested me?

Celiac disease is under-diagnosed — many people with symptoms go years before a correct diagnosis 2Ref 2National Institute of Diabetes and Digestive and Kidney Diseases (2023).Celiac Disease.Under-diagnosis of celiac disease, importance of gluten consumption before testing, and consequences of a false-negative result on a gluten-free diet. If you have ongoing GI symptoms (diarrhea, bloating, abdominal pain), fatigue, unexplained iron deficiency anemia, or a family history of celiac disease, it is worth raising celiac testing with your primary care clinician.

You can ask specifically: *"I would like to be tested for celiac disease. Can we start with a tTG-IgA and total IgA?"*

If the test is positive, or if your symptoms are complex, a referral to a gastroenterologist for endoscopic biopsy is the next step. Gale's primary care team can order the initial blood panel, review the results with you, and arrange a GI referral if needed.